You can see which cards are summoners vs monsters on steemmonsters.com while viewing your collection. Currently there is one summoner for each color/element. More details about how the different types of cards will work will be released soon with the full gameplay mechanics and stats.

As for your second question, the cards being used are not published with the "sm_find_match" transaction, only the hash is published, so it's not possible for the protocol to verify them at this time.  Most UIs, however, will enforce proper team creation prior to publishing the "sm_find_match" transaction so I expect it will be very rare that invalid teams are revealed.