Most non-championship 'cross races most places in the country allow mountain bikes, w/o bar ends. Most people in most of these races are riding 'cross bikes - for a reason. I have done a few races - deep snow, e.g., - where mountain bikes probably had the edge. If it's a good 'cross course, 9 times out of 10, the advantage will go to 'cross bikes.

And even if that wasn't true, lighten up and go race.