I've done it a couple times with the basic 13 oz. exterior canvas...the first time just because the installation tech said it could be done...and he was right! Only had a few banners I've done it on, because the 'stock' material isn't smooth both sides. But for banners it was fine-no loss of detail, just a texture that showed up. I was worried about the heated platen pulling ink off the banner from the first side printed and it didn't happen.
You do have to figure a mark on the banner edge to line up with the 'strip' under the pinch wheels so you have a reference point for both images to line up but don't cross your fingers for dead perfect line up on each side!