I would argue Yes.
Lay on Hands is a supernatural touch attack, meaning that it follows the rules of “weapon-like spells” found in Complete Arcane (yes, even though it is not a spell). These rules do not cover Smite Evil specifically, but generally clarify that touch-attack effects are effectively weapons in all ways but name – that is, if something enhances “weapon attacks” or “weapon damage” (e.g. Inspire Courage), it won’t work, but otherwise the touch-attack effect works like a weapon. Sneak Attack, for example, is explicitly called out as working. Rules Compendium clarifies further by saying that someone who has such a touch-attack effect is considered armed.
So in general, any touch attack that deals damage should be treated as a weapon in all but name. You make attacks with it, and things that improve attacks affect it. This should include Smite Evil. When you take your standard action to use Lay on Hands, you make an attack, which you may choose, at your option, to modify with Smite Evil by expending one of your daily uses of that ability.
Now, Smite Evil does say “normal attack.” What does that mean? No one knows. It’s not a defined game term and it’s unclear what counts as normal and what does not. Ruut’s argument that it means the Attack Action, which is used as a standard action, definitely seems wrong: not only is “normal attack” not the term they use for that (for that they say Attack Action), it also has pervasive impact on the paladin in general, making Smite Evil completely useless, rather than mostly useless. Jack’s argument that touch attacks are not “normal” attacks is more tenable – the rules, awkwardly enough, don’t have a good way to specify “not-touch attacks,” but ultimately this seems extremely flawed to me as well: does this mean a paladin cannot use Smite Evil in conjunction with a brilliant weapon? I don’t think so.
Ultimately, the paladin is a very weak class, and both Smite Evil and Lay on Hands are very weak abilities. The rules are ambiguous, but it is a very minor advantage to allow it, for a class that desperately needs every advantage it can get.
The Frightened condition, emphasis mine (PHB, pg 290):
Frightened
- A frightened creature has disadvantage on ability checks and attack rolls while the source of its fear is within line of sight.
- The creature can't willingly move closer to the source of its fear.
As you say, Dreadful Aspect specifies that the target is frightened of the Paladin. This is specifying that the Paladin is the "source of fear" from the Frightened condition. I'm not sure why this ability calls it out and the Abjure Enemy and Frightful Presence abilities don't, but the source of fear is clear in all cases.
The target will have disadvantage on attack rolls against everyone while the Paladin remains in sight.
Best Answer
Some yes, some no. And it's a surprisingly-even split.
There's no general rule on undead: either the Frightened condition (PHB Appendix A) or the Monster Manual's section on undead (MM pp.6-7, "Types") would be the places to look. But each specific undead's stat-block describes whether it is immune to the Frightened condition. (Is there any reason to why the list of undead that can be frightened seems counter intuitive? addresses the "why" of this.)
For reference, the MM has the following Undead which...
cannot be frightened:
can be frightened: