Whoo Boy Adam, you just opened a can of worms there!! Yes, it COULD be driveshaft related, could be a LOT of other things as well!!
Yes, it is fairly easy to remove the driveshaft! The hard part is getting it back into the u joint again. There is an inspection hole in the swingarm that once you push back the rubber boot you can see. This hole works dandy for sticking a screwdriver or something in there to hold the u joint end up to guide the driveshaft back into the splines.
My first thoughts when you stated they greased the splines is did they do BOTH ends of the shaft, or just spread some grease on the differential end only?? Ya never know...
The grinding noise can be a lot of things like a dry u joint, wheel bearings, brake calipers hanging up, warped rotors, clutch issue, and on and on...
You will get several answers as to what grease to use, I use a synthetic wheel bearing grease myself. You want something that is fairly thick as there is a lot of pressure exerted on the splines.