Since I am one of the apparently few people who plays Ultimate Team online (in fact it's almost exclusively what I play in UFC 3), I'm disappointed that it won't be there anymore. I am very much looking forward to an expanded Career Mode though, and I think the trade will be very well worth it!
I think the main reason for people not to play UT online, is the insane amount of griefers, who just exploit the game to make other players feel miserable. I understand that there is no way to ban them (unlike real cheaters, who luckily still get banned) and that normal players just resort to UT offline or give it up completely.
Thanks for all the new information, this took a lot of my scepticisms away, and I'm looking forward to UFC 4 even more now.