I'm pretty flexible on that.  On most things really.

I like the idea of him as sort of running with the same group for awhile, but if it fits your concept better I'd be fine with him sort of jumping from crew to crew pretty regularly too.  

If he's been around for awhile I could have fun with him being sort of a grump, grumbling about how things were better under the previous Rogue Trader if you want to do a bit about Valeria establishing herself, but I could also have fun with him sort of taking the opposite tact.  Maybe he didn't like the previous guy because he placed more constraints on Roald.  

Or if he's new maybe he's kind of a dick, doubting Valeria's ability due to her youth, or her sex, or just because he hasn't seen her take charge yet.  Could have fun with him talking out his ass and getting cracked down on for it.