In the past, I have had a compatability problem using a Futaba Rx and Jr servos, but I have not tried using them your way. I was using Futabe T6xa and T6xas transmitters and the rRx that came with each system on PPM.

I know that Hitec servos are absolutely compatable with JR equipment.

I presume that you are currently using a JR Tx and Rx, so the nautral assumption is that you are trying to save money by using less expensive equipment. Understandable, but, bear in mind that the attempt to save a few dollars in the area which controls your aircraft will sometimes cost a lot more in the long run.