The old Clone Wars Video Game from Pandemic uses the same models (or almost the same models) as SWBF and SWBF2. Some assets of buildings and props from the game, made for Geonosis, Hren Var, Raxus Prime, and Thule maps were released by Teancum, and some vehicles (such as the GAT, HAG, RTT and Cydon Prax Tank) were released by Psych0fred and in the ConvoPack vehicles. Where were these assets originally found?

the game's wiki
http://starwars.wikia.com/wiki/Star_War ... ideo_game)

Well, they're very similiar, but they aren't ripped from the game.
The Raxus prime props are modified Pandemic's assets.
Same for Thule and Geonosis. Teancum and all contributors did receive models and textures from many members, anonymous or not. The textures, especially, were sended to Teancum by contributors.
All vehicles you wil see on pshych0fred's website were made by psych0fred himself. He contributed a lot for the ConvoPack.

This said, note that some assets are 100% scratch-made. And if you use any asset from Teancum's secret files, you must credit Pandemic, Teancum and the TAW clan.

the assets are the original assets from the clonewars game. however they were not ripped but the original raw assets (in xsi) were taken and exported to battlefront by psych0fred and probably other people "close" to pandemic. psych0fred set the vehicles etc. up and released them but is not the original creator of them (as the readmes state).

I always believed that they were modified by the ConvoPack contributors.
So, aren't them... illegal?

no, because they were given to the community/members by people "close" to pandemic.
if they were ported without permission they would be illegal regardless if they were modified in any way.

The AT-XT is also from The Clone Wars game, exported by Psych0fred as well, I believe.