If it's a glass tank, I would. At least something like a yoga mat under the tank. Better safe than sorry and they hardly show at all.
BTW, I built my own 90g tank (36x30x20). It's rimless and no euro brace. But I added a acrylic base under the bottom glass and with a 'lip' that stuck out from under the bottom so all the side glass sits on the acrylic as well. And I added a yoga mat under the tank as well.
You can see it all in my build thread.