Tools | Infrastructure Management then under each appserver instance you should be able to see thread usage. (7.4 and 7.5 look a little different there in terms of how far you may need to drill in)
and there's a blcli command to dump this.
i don't know of a way to view it real time like a 'tail -f' type of thing. but it may exist.
Bill, is there a blcli command to dump the Infrastructure Management -> appserver instance -> Details information? (eg, BLManager Version, Started, PID...)
There are some unreleased commands: