There are very few shell providers that impliment limitations on botnets. Out of the ones that do, they limit the amount of connections, or how many listening ports can be used.
Those that refuse to allow any connections, other than telnet connections (including dcc) and IRC server connections, are a serious condender for the shredding machine.
As for IRC servers. No , 90% of IRC servers don't allow botnets. However, all the bots do not need to be ont he same irc network, infeact, they don't even need to be on a IRC server.
Beyond that, there is no way to tell, if 300 of the bots on there servers are connected in a botnet. They have no control or vision of this.
The only other option of thought there, is connecting all bots in the one botnet, to one hub. Besides being insane, slow, laggy and frequent timeouts, it's just not the way it should be done.
150 bot botnets run with a minimum of hastle and lagg free.