2007 Yamaha Grizzly 450 4×4 (Blue)

I see a nipple on the U joints, but there is no way to get my grease gun tip over it. Is there a special fitting for it or are you expected to disassemble the joint to lube it?
Also, are all the parts to lube on the U joints internal and sealed? Meaning, is there any reason to spray lithium grease on the outside of the U joints?
Thanks