I don't see any problem with belt and omni. After last year, my team has preferred belt over chain and I am quite pleased with the KoP setup for this year's game.
Do you have any specific reasons for using omni wheels? I'm curious on your design requirements that dictated their use.
Can you provide the wheel that you are using?
I'll suggest you look at supply of pulleys for the belts (look for nylon ones). Last year, we had a difficult time getting the pulleys and belts in the sizes we needed due to stock issues. You'll need to get them correctly sized for the belts you are using. Gates has a pulley calculator tool on their
website as well.