Can we be sure that leptons and baryons gravitationally attract each other?

Yes, we can be sure that leptons and baryons attract each other. Eotvos experiments and other tests of the equivalence principle give null results to about one part in $10^{11}$ these days. Under your hypothesis, different chemical substances would have different gravitational accelerations, and therefore we would get violations on the order of one part in $10^4$.