Yes you can use both large roach baits and small roach baits at the same time.
There is no problem with using large roach baits and small roach baits simultaneously to control large and small species of cockroaches.
Uses for Different Pest Control Products:
Combat has a variety of roach killing products to eliminate your cockroach problem. Combat® baits are easy to use and need no activation. Just place a bait station down where you have seen roaches - places like tops or insides of cabinets, along baseboards, or in bathroom corners.
Combat gels are ideal to use in difficult-to-reach places around your home. As a form-fitting substance, you can squeeze it into the small, narrow openings that cockroaches typically enter the home through. Place Combat gel in places like: behind the refrigerator, underneath sinks or inside cracks and crevices.