The physical results of infection are laid out for us. Perfectly fine. It doesn't have to change the volitional component in some player's roleplay of some Infiltrators willingly taking on the symbiote and thus maintaining their personality in cooperation with the creature, rather than overriding it entirely (though this is all at the whim of the Nom in question still). This definitely isn't the case for the vast majority of them, but could potentially be the case for the possibly loony willing sympathizers that cross that threshold. It's still one with you and you can't remove it (and thus, die), but the relationship remains the same.
This is an approach with some history preceding the Vagrants' existence if I've heard right, and has happened with some regular Nom-aligned Wild players as well in ancient days. Those specifics don't really seem to be validated / rejected either way by OP, just that the host is dependent on the little bugger, which I think most people assumed already. Plenty of room to work in.
Spacebound Nomads lack any ability to indoctrinate and dominate human minds; thus, they cannot turn anyone into a Thrall. Only Infiltrators can make them.
When we get right down to it, aren't Nomads communicating psychically with humans at all a fanon construction of Discovery just lent legitimacy over time? They definitely don't do any such thing in Freelancer proper iirc.I don't mention this to express any distaste for the concept and I find it neat, but I'd wonder why their spacebound form is less capable of the long-term, gradual indoctrination process if they're capable of that with a much smaller, more concealable form. The main advantage of the latter obviously being that it's hiding in a person, and isn't a huge alien thing that you're not likely to tolerate being alive long enough for it to matter.