Subfloor can be anything I want. I am going to remove it when I do the remodel.Then I would check out all the joists if you can get to them to be sure they are solid. Poking them with an ice pick is a good test. They should be hard.
Also how thick is the flooring and sub flooring? Is it all in good shape?
Your problem in this installation is the tub's individual feet. All the weight is going to be concentrated in only four small areas rather than spread out across the floor.