theres the faceless masses of crew and houseguards /voidsmen / random fighting man hired for the purposes of generic guard which is fine and easily abstracted with the crew rating although what i have tended to do is where a group of troops etc has been better trained -veteran elite etc then the relevant skills are increased to represent that so an armsman would have a BS of 60 for elite but the other skills stay at the original 30. but when shot they fall over and die without needing to track wounds etc.
Thats fine for large numbers of troops but when the rogue trader finds/handpicks and gets trained /implanted/equips a small group of utterly loyal bodyguards then the crew value kind of falls over as its too vague/abstract at that point.
I think i may have a look at the minion route. I know the player wont abuse the bodyguard and indeed it has caused several issues already because the bodyguard are utterly loyal to the trader and will not respond to anyone else if the trader has given them orders. (best quality volitor implants). i'm more than willing to kill the bodyguards off, but suspect that in character/npc terms because of the way the trader treats even the lowest born crew member there would be more than a few voluteers to replace losses (with long intervals for the training in their new duties etc)