Veronica doesn't leave if you tell her to quit the Brotherhood during her quest.
Thats odd. I completed Veronica's quest, and told her to cut ties with the Brotherhood. I was kinda pissed at them so I went into the bunker (left her outside), and killed everyone. When I got back out she was all mad at me, and told me to add her to my list. Was this a bug because I thought at the time I was doing her a favor... >.>
I for one really hope Ulysses turns out to be a pro-Legion companion, but I highly doubt it. Out of 2 DLCs how many companions have we been able to take with us? Also from the way they are building up the back story of the Currier, and Ulysses it does not sound like it will be resolvable any way, but one... with his dead body on the ground, and his loot in our pockets.
As for Victor as a companion for Mr. House people... On my first run I was so sure he was going to be our first 'real' companion. Then when I meet in again in Novac I was sure I had done something wrong. I was heavy on the NCR side of things so I figured I may have pissed off Mr. House. It is the only time I have looked up anything before my first play through in a Fallout game, but I was sure I screwed up somewhere because I could not get Victor as my companion, and I wanted him so badly. After a bit of searching I returned to New Vegas rather sad, and disheartened.
@ Lord Coake half-literate is still better then 99% of the rest of waistland