Hey Riley,
To be honest, the Kent reactor is certainly not the best choice for BioPellets as a recirculating reactor works much better but it can be done. You will need to get some plastic screening to put at the top and bottom (remove the foam). Without the plastic screening the pellets will get through the grid that is currently in the Kent reactor. The plastic screens can be purchased at Michaels (in the knitting section I believe) and cut to size.
As for running the GFO and Pellets in a dual reactor off the same pump, I don't suggest it. First off, the BioPellets will need a much higher flow rate than the GFO to get them tumbling properly and it's going to be near impossible to give both the flow rate they need with such a setup. Second, the bacteria and slime that comes off the bioPellets will clog up your GFO if ran consecutively.
I would suggest running them off separate pumps.
Hope this helps....
Stace