No, glass does not need to be sealed. If you have hard water it will show & a good cleaner will be needed. Just like a glass door, it can be hard to keep clean.

Hard water stains can appear on shower glass tiles. It is nothing but whitish looking deposits formed when minerals react with hard water. Although you can remove stains and get a clean surface after using tile cleaners, you cannot guarantee that staining will not occur again, and so it is important to seal the tile. I found the utmost satisfaction in this natural stone sealer called Celine. It seals the tile and further prevents it from getting stained and is quite effective in removing all the minor scratches and gives a sheen to the surface.