HI,
I do know that at one time non Google mail account could also be made to work in iChat.
It tended to be with Google account that ended google.com (This was the server name as well like regular Jabber IDs)
These used port 443 as well.
This has been stopped and only Google mail accounts can have "Talk" enable AND work on external Clients.
I remember that I was convinced I 'knew' my email ID without looking it up as I had it set up in Mail as a POP account.
I had issues when I switched it to using IMAP and had to look it up and found I have the other type to the version I had in Mail.
Due to this I did actually try both ways in iChat which is why I know it does not work.
I am not familiar with a GAPPS account.
The other things I would try in Messages or iChat is to tick the "Automatically find Server and Port" and see it that gets a Login.
9:48 PM Saturday; July 28, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
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