I am not familiar with CaribSea Aragonite, and have never used it. However, if it is true ARAGONITE, then it is one of the various crystallization forms of CaCO3 (calcium carbonate).
If placed in relatively soft water with pH below 7, then aragonite WILL dissolve some (albeit slowly), and thus it WILL affect the pH, by elevating it and by increasing total hardness. If it is placed in harder water with a higher pH, it will help to maintain the higher pH (buffering) and should not dissolve.
So, it is important to consider your tap water characteristics, and the type of fish you want to keep to decide whether aragonite is a desirable substratum.
I don't keep rays either, but I would think aragonite will NOT be a desirable substratum for SAmerican freshwater rays, due to its effect on water characteristics. I would also think it may be too rough on the rays, but I have no experience with that. Hopefully others may have complementary suggestions.