I have pulled up many tubs & shower pans where that was used, and I don’t think it really did much for support. Some of the pans I pulled needed replaced because of a crack (great stuff used instead of mortar)
I also have never seen a recommendation from a manufacture to do that.
This tub can be set with a mortar bed. I would mix the mortar fairly loose if you are not needing to overcome an unlevel floor. This way you can easily get the tub to set in place.
That being said, this tub is not requiring mortar unless its unlevel. So this may be a fairly solid tub to begin with and may not feel the need to mortar it in place