Is summoner monk on the banlist?
A quick search on the Current Official Banlist we can see that he is not on the list at all. 

This means that it is Unrestricted, and you can use up to 3 copies of it in your deck builds.

However, also according to that Official page, seems that next Ban List is soon to come (this month), so there could be a chance the status of Summoner Monk changes. 



On another note, I have always liked Summoner Monk, and the fact that it is at 3 copies may strengthen some strategies out there. It is particularly useful to decks that have a high Spell Card ratio on their builds or that focus on Lvl 4 Xyz summoning (Harpies, Spellbook, Rescue Rabbit, Noble Knight, Gladiator Beast, and many, many others.). 

In the case of my Harpies, this is a great addition to the deck, as it enables you to pull any Harpie (specially Harpie Channeler) from the deck. The best possible scenario is to pull a Summoner Monk and activate its effect by discarding Hysteric Sign. 

This means you get to summon a Harpie from the deck (opens many plays with Channeler) and at the end of the turn you get to search for up to 3 Harpie cards by effect of the Sign, refilling your hand for further combos next turn.