Monks don't inherently know when they've been charmed, but we do still need to allow them to use their abilities. (From a Rules As Intended perspective, the monk wouldn't have this ability if there were no way to use it.)

I recommend you rule that, although the monk's conscious mind doesn't know when it's been charmed, the monk's subconscious can recognize the charm and can choose to remove it.

A vampire's destruction doesn't end its dominion

Broadly, an effect ends when the effect's description says it ends. In the case of the supernatural ability dominate of a vampire (Monster Manual 250—3)—that functions much like the 5th-level Sor/Wiz spell dominate person [ench] (Player's Handbook 224—5) except with numerous exceptions—this is, if allowed to run its course naturally, typically 12 days. (Any vampire's effective caster level for the dominate supernatural ability is largely fixed at 12. The effect can, of course, be used again on the same creature prior to the conclusion of those 12 days to extend the duration.)

As per the spell dominate person, the vampire each day must take a 1-round action to concentrate on the affected creature. Failure to do so means the dominated creature receives another saving throw against the vampire's dominate ability. If the dominated creature fails this saving throw, the dominate effect continues, while success means that the dominate effect ends. Similarly, a vampire that issues an orders to a dominated creature that goes against the creature's nature grants the dominated creature a new saving throw, and the creature gains a +2 bonus on that saving throw. Once again, if the dominated creature fails this saving throw, the dominate effect continues, while success means that the dominate effect ends.

Also as per the spell dominate person, a vampire on a different plane from creatures that its dominating can't issue new commands to the dominated creatures. However, even while the vampire is on another plane, its dominated creatures continue following the vampire's last issued orders. A vampire's trip to the City of Brass doesn't mean party time for its thralls!

As it's a supernatural ability rather than a spell or spell-like ability, a vampire's dominate special ability can't be removed using an effect like dispel magic et al. The 1st-level Sor/Wiz spell protection from evil [abjur] (PH 266) and other alignments specifically don't prevent a creature from being targeted by dominate effects, but such effects are suppressed while such a spell's duration continues, and the protection effect—if employed on an already dominated creature—for its duration suppresses that dominate effect and prevents the controller from issuing new orders. This is, unsurprisingly, likely little consolation to the dominated creature. (The spell protection from evil's duration is only 1 min./level.)

The vampire's supernatural ability dominate is one of the most powerful weapons in its arsenal. This DM has, in the past, gone so far as to house rule the dominate effect ends when the vampire's destroyed as the question describes, and he's even allowed effects like dispel magic to remove the effect as if it were a spell-like ability rather than a supernatural one. A by-the-book vampire that dominates a PC essentially removes from play a PC that possesses a low Will saving throw bonus until what can be over a week after the vampire's destruction: the still-dominated PC desperately attempting to fulfill the last order his master issued, and the other PCs scrambling to use protection from alignment effects on the dominated PC so all the PCs can continue the adventure. While this may be interesting once, I've found that repeated encounters in the same vein kind of suck.