If Burn has been betrayed, then I would say he would make a good friend.
It is quite easy to see that the general Ipso population isn't exactly friendly and loving to the probes. They are treating them like far less capable children, and new technology that they can resarch, exploit and then destroy. Burn has seen the truth about the probes, and has probably been ruled as borderline insane by the Imperium. He must be quite important to have maintained his position (at least to outward appearance). If a similar situation had happened hee, Burn would have been drummed out of society.
He has risked and lost a lot to help our probes, and I would certainly say we can trust him. As for the remainder of the Ipsos, I would not trust them as far as I can throw them.
Hamlet