I see people bringing rental
ECVs into TL all the time. As long as you don't try to drive on sand there is no problem.
At the water parks we have a limited number of standard wheelchairs available for loan (must leave a CC or DL as security) at no charge. However, these also cannot be drivn on the sand. There are also a few beach wheelchairs, but these are only for temporary use for someone who needs one to get into or out of the water.
And you may be able to do the lazy river.