I think that there are two other clues that V'Lane is an Unseelie Prince:
1) In the museum, he asks Mac what they stole from O'Bannion. They knew she stole something, just not what it was. One way that 'they' might have learned those facts - namely the fact that there was a theft and not what was stolen, is if the 'Rhino Boys' that were staking out O'Bannion's place worked for the same outfit as V'Lane. The rhino boys would know that something was afoot, but probably not what it was.
2) When she pulls out the spear, he vanished right away. He didn't say - oh, good! You seem to have something to protect yourself with now, and won't be needing the Cuff of Cruce after all.
