Can this be used to install a Glue-Up/Glue-On bathtub/shower surround?

Yes, it is possible to use the Loctite Power Grab Ultimate. However, the instructions do not speak to installing a bathtub/shower surround therefore the successful use will depend upon the wall surfaces and use of temporary blocking until the adhesive is fully cured. Note that this product is not a trowel grade adhesive if your surround manufacture instructions indicate troweling is needed. Unfortunately, in these situations the user assumes responsibility for intended uses not spoken to.