Its also worth considering:

-who the meeting is between - is this a meeting between the "leaders", or representatives (the higher it goes the more political the implications)

-who else knows about it (public or private), and can use it to their advantage, or your disadvantage - gets to Niel's point about legitimacy

-what is the intent of the meeting, and what is the bigger picture. I had advised an Iraqi leader to invite someone we both knew was bad (but could not prove was bad) over to talk, but the purpose was to collect additional information and to provide him with some disinformation. We agreed that at some point in the future this guy was going to slip up and we would have the confirmation we needed to disrupt his activities, but at the moment I felt it would be good for us to "know your enemy" so to speak. It was a controlled situation where we discussed the way the conversation should go several days prior, and guided the dialogue during the discussion, and largely accomplished our goals. It was also targeted and tactical in nature, although this person was developing into an operational player.

Best, Rob