My friends and I regularly multiboxed DAoC. In fact, I believe that was part of their monetary strategy because there was no other use for buff bots except to sit in the keep on another machine while we send in our $15/month for that account. Based on that I would suggest that it will be okay, but it's really hard to tell because at first GMs are going to encounter this behavior and it's highly likely that they are not going to have a policy for it and the actions that the GMs take will vary wildly.

We also would drag several toons around with us while XPing, but I don't think it ever occured to us to actually have them do DPS since certain classes were already hugely OP in PVE at level 50. We did have a keyclone-like program that we used but mainly that was used to do autobuffing.