This has nothing to do with ULX, UTeam or even ULib for that matter.But, because one of our team members released a popular addon for ULib that changes player teams, and we constantly see this question where ULib or UTeam gets blamed for it, I thought we better place it in our FAQ.
For some reason, your server console variable sv_alltalk is set to a number that prevents all teams from hearing.
Place "sv_alltalk 3" (no quotes) in your server.cfg file and/or console.
If you have voice enabled, this variable allows all players to hear each other no matter what team they are on.
EDIT 4/29/2015 - JamminR - Per conversation, I learned sv_alltalk levels changed - updated to reflect change.