So I bought a used xt derailler off ebay and I have been preparing to install it on my bike. One thing that I've noticed is that compared to the Deore derailler on the bike these jockey wheels seem to have a great deal of resistance to spinning. They turn just fine but it takes more effort to make them turn. Is this an indication that they are worn out? I can see about replacing them but I only want to do so if necessary.

Have you tried taking them off, cleaning and lubing them?

I believe they have rubber seals, which won't let them spin, but the actual drag is almost nil.

I did try to clean them and lubed them using some grease. They still have some resistance to spinning. The jockey wheels on my deore will spin quite freely if you flick them. I guess I can just install the derailler and see how it behaves. Doesn't take that long after all....

Edit:

Alternatively, I suppose I could switch the jockey wheels between the derailleurs if necessary right?

I'd probably just run it as is. Chances are it will free up.

Are you sure it isn't the viscosity of the new grease that is slowing their rotation?
Your older wheels may be spinning more freely because the lube is old or dried up.