Is it OK if some of my wrist shows with the honor guard coat while saluting?
As long as you are in compliance with the following, it doesn't matter what happens when you are saluting.
CAPM 39.1, Pg 31, Para. 4.1.5.2. "With arms hanging naturally, sleeves will end ¼ to ½ inch
below the wrist. The bottom of the coat will extend 3 to 3 ½ inches below the top of the thigh."
If your wrist doesn't show when saluting then you sleeves are probably too long. capmaj posted the reg reference about how the sleeves should be.