Potatoes are used to make vodka, and corn ( maize) is the basis for corn liquer. But are either ever used to make a non-distilled alcoholic beverage? What beer is to whiskey in the case of wheat? If not, why?
In and of themselves, no. But corn is the basis for bourbon, and is a component of any number of cheap American beers. Burgie comes to mind most readily. But the wort still needs 2-row barley to provide the enzymes to break down the sugars in malted corn.
I don’t understand your second question at all! 
Were you asking if there are any alcoholic beverages made from wheat, of course there are. Weissbier, Witbeer, Berlinerweiss, etc. are all wheatbeers. Maker’s Mark bourbon gets its characteristic smoothness from wheat.
[url=“http://www.indepthinfo.com/potato/wine.shtml”]Potato Wine**
[url=“http://winemaking.jackkeller.net/reques89.asp”]Corn wine**
Just to clarify, though I’m sure you know this - “wheat beers” are only partially wheat, with the rest of the grain involved being barley.
Rice is another “filler” grain whose extracts are added to some cheap beer types. IIRC, sake is not a distilled beverage, and this is also made from rice.