Does anyone use a split ring or snap on this lure or is tying directly to the lure the best way to rig it?

I do not. There is no pivot or swing to the lure’s action so there is no benefit to do other than tie directly to the lure. 

I use a swivel to prevent line twist if the body spins instead of the tail.

I tie direct.

Get rid of your wopper ploppers  they do not work....

Tie direct, no benefit to adding a ring or snap plus it adds weight to the front. 

The only time I have an issue with the bait rolling is when something is out of sorts on the bait. Grass will get tested up in the bait at times and hinders the freedom of the plopper to do it's thing. Clean it out and you should be good to go.