The d20 class rules are flexible enough that there isn't much need for specific classes by faction; class determines professional skills. (It's a design principle of d20 that anything focused enough to be faction-specific should be a prestige class. Officers of any military could have Noble levels, for example... when you get right down to it, being a scout or fighter pilot is the same whoever you fight for.) There are some good examples of this scattered across various rulebooks.
That said, the Hero's Guide is the faction-specific-characters book, and has several prestige classes particularly aimed at Imperial characters:
Black Sun Enforcer, Black Sun Vigo, ISB Special Agent and Sienar Engineer.
A few other prestige classes are good matches:
The base military classes: Elite Trooper, Officer, Starship Ace (Main Rulebook)
Bodyguard (in the Ultimate Alien Anthology) or Loyal Protector (Hero's Guide) are good for Imperial / senatorial guards.
Chief Engineer (Hero's Guide) is another likely example.
The Hero's Guide also offers some good example builds for an Imperial Officer using the standard Soldier/Noble/Officer classes. It's probably the best answer to your question, as it also has some relevant feats (Aristocrat's Honor, Combat Veteran, Diplomatic Immunity, Gun Crew Chief, Political Pull, Flight Academy Training, Imperial Command Training) and the faction rules/ideas.
Also, two Pre-RE prestige classes are specifically Imperial: The Emperor's Hand and Imperial Inquisitor (both in the Dark Side sourcebook). Both should work with minimal conversion in RE.
(Also, the Rebellion Era sourcebook obviously has a lot of general information and character templates. No classes though, unless I remember wrongly.)
To begin with, the D6 space rules actually differ a bit from Star Wars D6. I'm not sure if it matters for this particular question (I haven't fully read through D6 Space), but it's worth being aware of.
This answer is based on the Second Edition, Revised and Expanded rules (Color Millennium Falcon cover; the most recent prior to D6 Space).
Basic Targetting
For ranged, the difficulty is based on the range to your target (page 88). Point-blank is Very Easy, medium range is Moderate, etc.
The actual distance defined as point-blank, medium, etc. varies from weapon to weapon. For example, a Bowcaster is listed as having a range of 3-10/30/50. This means that 0-3 meters is point-blank, 3-10 meters is short range, 10-30 meters is medium range, and 30-50 meters is long range.
For melee, the difficulty to hit is listed on the weapon (page 89). A vibro-ax is a moderate difficulty to hit with. A knife is a very easy difficulty.
Resisting Targets
Characters can use reaction skills to make themselves harder to hit (page 79). This is generally going to be either dodge, melee parry, or brawling parry.
When someone attacks you, but before you know if they hit, you can declare a reaction. This uses either one of your pre-declared actions or can be a new action (your choice). Multiple action penalties apply to the reaction, and if you make it a new action while you have other actions remaining the reaction adds to the multiple action penalty for those additional actions.
The reaction roll replaces your base target number to be hit. Even if it's lower. And it applies to all further attacks of that type in the round. A bad reaction roll can potentially be bad news (although the difficulties in ranged combat are generally pretty low to begin with).
The reaction skills are summarized on pages 89 and 90. Note that dodge is exclusively for ranged attacks and grenades. Ducking out of the way of a knife is brawling parry, not dodge.
Modifiers
There are a few modifiers that apply on top of reaction skill use.
Unarmed vs. Armed -- When armed, attacking or parrying against an unarmed opponent gains a static bonus (melee parry gets +5 vs. unarmed opponents, brawling parry grants armed opponents a +10 bonus). Just add this in when it's appropriate (page 90).
Cover -- Usually if you have cover from one person, you'll have it against everyone. When this isn't the case, you have a few options:
Roll the dodge and cover separately. Keep track of both numbers and apply as appropriate.
Roll the dodge during the first attack. During each attack impacted by cover, have the player roll his cover dice whenever he would otherwise be hit.
If the attacker beats the target number to hit the character (i.e. their dodge in most cases) but misses due to cover, they hit what the character was hiding behind. If it's something that can be damaged, they roll to damage the cover (page 93-94).
Full Reaction
The final piece to the reaction skill puzzle is full reactions. This represents going entirely on the defensive. A full reaction can be the only action taken in the round, but adds the base difficulty to hit to the reaction skill (page 90). Note that a full dodge precludes parrying (and vice versa).
Best Answer
Yes.
You've read the rules correctly and a weapon does indeed always do at least 1 damage more than its written rating when it hits, before subtracting soak.
Why?
As with other game systems that use similar mechanics (Shadowrun's net hits are very similar to uncancelled successes) the game rewards a good attack roll with increased damage. This makes sense in simulationist terms as well: the good roll represents a particularly lucky shot hitting a vital spot or similar.
While this mean that a weapon does always do higher than its listed damage it's quicker and easier to calculate damage if you don't have to remember to subtract 1 each time.