Well another thing would be to have them post under their own name like you seem to be suggesting Timelord, but I am thinking that if they are my agent(s), then they should post under a Nym that I am able to control and that clearly states the relationship.
If they can post from the account, you don't control it

If they make their own account, you can leave neutral (
or if you trust them even positive) feedback stating the relationship. If they quit, you remove (or update) the feedback.
Sharing accounts also means
disclosing IP addresses of all users.
otherwise it is too ambiguous, too weird, and even likely to have backlash on me, too... and maybe even harder to keep track if there were to be multiple accounts (besides starting out with one)
I assume you'll need to keep track of your agents anyway. This way, at least you can distinguish who does what.
I will have to ponder on this whole topic a bit more. I would only be starting by adding one at a time, and then if at some point there might be more than one person helping me out, then at that point I might want to consider whether it would be feasible for them to share the same account that had been established for that, or if a new account might be in order. I think that some of it will become more clear once I write out my OP in regards to why I created such an account and the thread that I intend to create that would end up being the work of such account (and hopefully would grow and evolve with the passage of time).. I don't know how much of a teaser I should give, but it has to do with figuring out how to fund projects and then to subdivide various accounts that would be used to fund such projects.
By the way, how do you find the IP addresses? I would have thought that ONLY admins would have been able to see that kind of information... any member can find that kind of information?