The manual says "Replace U bolts to anchor plate and tighten nuts securely."
I've wondered if they can be reused if the U bolts come off with no problems and are in good condition or if they need to be replaced with new ones?
Bruce Yes, as long as the old U-bolts are in good condition, they can be re-used.
"Replace" simply means to put the U-bolts into the assembly, and makes no difference whether you are using good condition previously-used U-bolts, or new ones.