I have a Futaba 4VF radio with the 4.8 v 1100mah NICD, I recently purchased an additional futaba 4VF; however, it came with a OFNA 1600 NIMH which I believe is 6V. Is this still an acceptable battery to use for this radio?

Short answer is yes. Actually the 4VF uses a 9.6v battery. The receiver is what will use the two packs that you are refering to. Most receivers (including the ones that came with the 4VF ), will work just fine with either a 4.8v or 6.0v battery.
Paul

After searching some more it appears this application is used mainly in rc cars, anybody confirm? It's a 5 cell battery pack

It may be sold for a car but it will work fine in an airplane. Most receiver sand servos are compatible with 5-cell/6V batteries. My main concern would be the battery condition. How old is it? How many times has it been charged? What is the actual capacity? Cycling is the best way to find out the battery condition. Still, if you are in doubt, new batteries don't cost all that much when you consider the alternative of losing an airplane.

OFNA is big in the car/truck scene..I don't think they make anything for planes.....6V will make your servos faster and supply more torque

If it is sold for a car, it is designed for a car. The radio will have a ground channel crystal in it which cannot legally be used in a plane. In order to use it in a plane it would need to converted to an aircraft channel. Good Luck, Dave

The radio itself is channel 46, just unsure of the battery application and history.

Check what frequency it is on. If it is 75.XXX it is surface use only (cars, trucks, boats), if it is 72.XXX then it is for air use. The reason for this is so that the local guy at the park down the street running his R/C car doesn't unexpectedly shoot down the other guy flying his plane.
Curtis