Humboldt brewing company makes a hemp ale, it tastes alright but not worth the price, so using pot seeds in beer should work.
But I'd reccomend using barley as well, both for taste and as stinkyattic said sugar.
Although alot of brew shops carry bags of sugar (not sure what kind of sugar) that is ment to be used for fermentation, so it may be possible to cut the barley out completely. I have tried homebrew made from wheat, and rye (no barley in either) and the wheat ale tasted ok, but the rye ale tasted like shit.
I say give it a try, if I had an abundance of pot seeds I sure would.