If the Buddy is a Jabber Buddy (this includes GoogleTalk and Facebook IDs) then you will not be able to Video Chat to them unless they are also logged in via iChat.
Basically Jabber use a different Internet Protocol than iChat to Connect.
This is called Jingle and is a part of some Jabber apps but is also part of the Web Browser Plugin you can get from Google and their PC Standalone app called GoogleTalk as well.
Google's version is actually not that compatible with other Jabber apps (See Here)
I do not have a Facebook account to know how they do the Video bit but it will be by using Jingle.
If this does not cover the issue you are having please tell me the account types your are using.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously