If I had 50 farms, I could create 50 accounts... or more likely I'm not going to want to maintain all those accounts and would simply want one account to manage. I believe this makes more sense, given you can simply filter your queries/reports using a secondary sorting dimension. Simply set your secondary dimension to be
Content>Host and then by using an advanced filter or custom segments, you can see stats for each server. This assumes each has a unique url or IP.
If all farms are redirected by a load balancer, you might need to set a custom variable to be your farm instance, in which case this would become your secondary dimension.
Not ideal, but preferable to maintaining multiple accounts. The downside is that when you want to do some analysis on a secondary dimension, you lose that ability.