Loud HH, soft snare!
Yeah, that can definitely ruin your day, and be a problem .. .especially among drummers that are not that experienced in recording in the studio-- I have to say that I was among those 'troublke makers' who would play heavy on my hats, and lighter on my snare-- until I got my act together, and worked on my dymanics .. . its all about experince.
But, I have to agree with 'Track Rat' smaller hi-hats would be the way to go, and my first choice-- like a pair of 13's-- Try to stay away from the Zildjian Z's for recording (vert loud hats) However, sometimes you dont have that option of changing HH's.
Also, it depends on what type of music your recording, and the drummers playing style-- If he is playing the hi-hat slightly open on most of the tracks all the time-- without too many dyanmic changes, its going to over power your snare all the time! Try to convince him to experiment with keeping the hi-hats closed when keeping time with the hats, rather then that bashing sound of slightly open-- it will limit the overtones and wash slightly.
Also stay away from piccolo snares with a drummer that is too hard on HH's, and too light on the snare-- try a 5 x 14, or even a 6 1/2 x 14, depending on the music-- even though I think that the piccolo snares are the best! type of snare to record with-- other than the Ludwig Supraphonic-- it becomes too shallow and weak for a heavy HH hitting drummer.
You might want to try micing snare from the bottom-- (pointing away from the hats), and experimenting with that-- a lot of engineers stay away form micing the snare from the bottom, since it brings its own host of new problems to the table-- But, given your situation-- it might be worth a try.
Lastly, if you have an extra mic-- place it pointing right at the High-hat-- you wont be recording the hi-hat mic to the track-- But, just using it similar to a Scratch vocal, or scratch instrument mic) load up the volume as high as possible on the HH mic, and rig it so it is just getting pumped through the drummers cans-- trust me, he will start backing off the high-hat quickly enough .. .it sometimes forces the drummer to lighten up on the hi-hats, and play with more dynamics. . . Anyway, Good luck!!