I have had no problems in the past. I would not recommend using a brand new reamer but I was able to ream 16x 1/2" holes in .25" plate that were laser cut without an issue. I c'cunk by hand first then floated the part (not in a vise, not clamped to the table - chocked against a post) to let the reamer remain on center - the tolerance was not super tight and the fit was acceptable.
I have also tapped lasered holes in 3/8 plate without issues. If the laser guy gets the set up right, the edge quality is very acceptable and the HAZ is not really all that great. If they penetrate on the diameter you will have a problem, but if they penetrate somewhere in the middle and iterpolate to the diam you will end up with a relatively smooth hole. If you are handing them the data, do this for your holes.
No problems reaming or tapping due to hardness, though. I have not dealt with anything thicker than 3/8" from a laser, though.