can you connect two or more controllers? Is it possible to connect two or more bluetooth controllers to one android tablet? I am wanting to emulate some games that are four players and I want to know if three friends and I can all play together?
This is a bit of an opinionated, and caveated answer. 

According to the Android Developers you can indeed 


  "Manage multiple connections"


It seems to be the case than an Android tablet can connect with multiple Bluetooth devices sending data only, but Bluetooth devices that can also receive data will only pair with one device. 

From my trying this on: 

Galaxy Tab
Nexus 9
Nexus 7
Galaxy S5  (phone not tablet obviously)
Nexus 10
Galaxy Note

It only allows one controller and disconnects the others. We had some patchy performance with two working, but Bluetooth is not a good technology for multiple connections like this.