You would need to give a softshell the option to bask, if for nothing other than giving them a spot to take a rest. They are not fully aquatic. Softshells are notoriously skittish when compared to other turtles, so you may not ever see the basking area being used (but it will be). I know that whenever I'm up at the lakes around here they are always out basking, but they usually bail back into the water well before you are anywhere close to them.