Not many species of tortoises are semi aquatic. Some species will utilize large water source. Semi aquatic turtles would be more benefited being kept in a paludarium. Then again it depends on which species and how you set up the enclosure. Typical set ups for paludariums are for like dark frogs or newts. I also would recommend against it because how destructive tortoises can be to enclosure decorations like moss, plants and fancy set ups.
Really depends on the species. Some species require a very established enclosure and prefer environments like paludariums. What species are you thinking of? Just remember that they space needed for the animal is more important than glamorous items in an enclosure. But hides and plant material does offer them a safe refuge for hiding and feeling more comfortable in it's surroundings. But it has to be done right. I'd say a good species would be a splengeri, or cuora species would benefit from those types of no closures and set ups.