It's still a bit odd that Aria would attach this much significance to one krogan, considering her status as Omega's queenpin for the last several centuries. Skilled though Vayex might be, they are kind of on very different levels, especially now that he's on the run; she has no shortage of other mercenary and criminal contracts to turn to, and unless I'm mistaken doesn't seem to maintain a very close contact with... well, anyone.

That being said, it's not unknown for her to take a liking to skilled individuals who respect her authority and perhaps help her out along the way - like Mordin Solus or Commander Shepard. I imagine it might be something like that. She can be grateful, though somewhat grudgingly. Her friendship may be a two-edged sword in that she may have some plans for him as well, though - why destroy the Blood Pack when you can eventually try and put an altogether more reliable kind of krogan at its head, if opportunity shows? Both asari and krogans live long lives, meaning there'll be plenty of time for such opportunities to appear...

I'll get back to you on abilities in more detail a little later. Mind you, krogan regen kind of falls under the krogan keyword anyway, unless you want to show that his is exceptionally potent. Something like Calm For a Krogan or Cool-Headed Professional would make a good ability too. Hated by Blood Pack would be a good flaw, as would that blindspot you mentioned.