
I would definitely have it raised. I don't have a hot tub but do have a rather large pool on the patio during the summer and two ponds. One pond is raised and the other is in the ground. Having a dog that would swim in your cup of tea if he could fit in it all sources of "leisure" water can be problematic :-)
It took a while to stop him swimming in the ponds although he has retrieved a fish from the bottom pond and dumped it in my lap whilst I was sitting enjoying the sunshine one summer. The pool is a different matter. The sides are higher than his head but it doesn't stop him from joining us if I don't catch the look that says "Wow I fancy a dip myself" :-)
31kg of dog leaping uninvited into the water with you causes a rather large tidal wave :-) and once he is in there he wants to be
on the lilo with you and that means an instant capsize. Normally he is very well behaved and a simple no or redirection is all that is needed but where water is involved he develops instant deafness, grins from ear to ear and it's tally ho folks make room for me :-)