Hi mcdeali,
I've got a tank with regular sized smooth gravel and my 4 very small kuhlis seem to have no trouble getting underneath it to hide in the plastic plant bases. They've got spots where they regularly hide in the gravel and leave just their heads poking out. As long as your gravel isn't sharp and there are no large gaps where your loaches could crawl under the UGF and not be able to get out again, I'm sure your tank would make a great home for loaches. In my opinion they're very fun fish to have, and like other loaches they react to swings in barometric pressure; if you pay attention to your loaches' behaviour you'll know it's going to rain before the weather man does!