How many connections reads queue
Sort of. You can see though sys.dm_exec_requests executing a RECEIVE statement (including a WAITFOR RECEIVE). By simply peeking into the the currently executing text sys.dm_exec_sql_text(sql_handle) between the statement_start_offset and statement_end_offset you can see if the statement is RECEIVE or not (with some parsing...). Figuring out if an active transaction has issued a RECEIVE and is now processing returned messages is more complicated. 

Is somehow of an unusual request, why do you need to know?