The topic of OW divers doing cavern tours without cavern certs can cause a lot of heated discussion, but this is routinely done in Mexico, with an apparently acceptable safety record. The agreement there is that the guide must be at least an OW instructor, full cave certified, and dive in full cave gear (doubles, long hose). The guide is to lead no more than four people. A guideline is to be run to open water.
I have heard that not all operators adhere to these guidelines, so it's worth asking the questions before you go.
In my opinion, you should have good buoyancy control and fairly horizontal trim before you do the tours, just out of respect for the cave. The formations in the Mexican caves tend to be small and fragile.
All that said, I think cavern tours are, first off, a magical experience, and second, an excellent way to find out if cave diving intrigues you enough to pursue training.