If you meant it might damage the tractor, I don't see it. However pulling with the FEL could put you on tippy toes in the front if you don't keep your bucket near to or sliding on the ground. I have pushed some large loads like huge rocks that I couldn't lift with my LS P7010 and had no problems, just put as much in the FEL bucket as would fit and pushed it along the ground. I also pulled out some huge trees from a pile that I couldn't get into with the tractor by hooking on to my chain hooks on the FEL bucket. I just put the bucket on the ground and let it slide back so it wouldn't tip me up on the front wheels. You just need to think a bit about the dynamics of the load and adjust accordingly. I would much rather be pushing a heavy load than trying to carry it with my rear wheels bouncing off the ground. I don't see this action any more that pushing into a pile of dirt till the wheels spin. Pushing or pulling, the FEL should be designed strong enough to take all that the tractor can put out in traction. HOWEVER, sudden impacts with immovable objects at a fast speed are not advisable for sure.
I don't pull or push a load by attaching it to the backhoe, EVER. Most tractors can pull more than the backhoe can stand so you can easily damage a cylinder or worse, the frame of the hoe.