A volus soldier is... an odd choice, but I suppose they must exist. :P The system isn't really very strict about what kind of abilities are available to you; it is reasonable to assume that a Soldier has access to special ammo and grenades, and so he does. Or you could specify it additionally if you consider it that big a part of your character (Special Ammo Expert? Experimental Weapons Contract?).

In the meantime, I've been adjusting and refining the premise that I have in mind. I think it really may be better if you are working for a top secret organisation, in contrast to the somewhat more public and overt Spectres, recruited in exchange for both money and the erasure of any past criminal records on Citadel worlds, reporting not to the Council directly but to your project's Director, and carrying out missions on the fringes of and beyond Citadel Space. At least, that's how you start...