Yes, different varieties of pawpaws will pollinate each other regardless of whether they're on their own roots or wherever they're placed. All that matters is that the wood that produces the flowers didn't come from the same tree.

Another option could be to get some flowers from the park and hand pollinate your tree until it makes it's own flowers.

Benny

Benny has the right idea....If yours is still flowering, collect some pollen from the grove. Here's a guide that's helpful:

http://www.clemson.edu/hort/peach/pdfs/fg97.pdf

This spring I picked some flowered branches from that grove and acted as a honeybee. I held a flower and carefully poked it together with the ones growing on my tree. The branches were left in a bucket of water under the tree for about a week. Time will tell.