Would it be ok to have two different makes of gravel in the same tank? The substrate is of the same size just a different brand?

substrate

You could even mix different sizes of the gravel if you want! Makes things look rather interesting My cousin has some rather fine gravel where the plants are growing, some coarser, and then something bigger than a pea, and they all look really nice together! But, do remember to clean it well under water before adding it to the tank, it's a great deal of pain to notice that it wasn't cleaned well enough when your tank is already filled with water, and all cloudy from the dust in the gravel.