combine coaches?

[m i n o]

hey guys i have only been watching the combine for the last few years so i still don't know everything about it. was watching last night and noticed many of the coaches running the drills were from nfl teams(saw a browns,sf,ariz coach) and i wondered how they went about selecting who runs these drills and if it was the same particullar guys every year(iv'e noticed john lott doing the weights every time ive watched the combine).
doesn't it give a slight edge to the team of the coaches as they get alot more hands on with the players?

thanks for any help to my questions..off to work so i'll catch back up tonight.