"Are the lug nuts exactly the same (as far as physical size) between the 01 and 99?"
My guess is yes.
The Mopar parts book for model year 2000 shows a single lug nut for Ram 2500's:
P/N 6034727 NUT, Hex, . 516-18, with WDV,WDZ
WDV is the 16 X 7. 5 steel wheel used on Ram 2500's.
WDZ is the 16 X 8 forged aluminum wheel that first appeared on Ram 2500's in model year 2000.
Also, the trucks that came from the factory with the forged aluminum wheels have a steel wheel for the spare.