Can 7D grip take OEM battery and 3rd party battery?

I am on the fence about buying a grip for the Canon 7D.

I was looking into getting the flashpoint version from adorama. I'm wondering if it can take a genuine LP-E6 battery and a 3rd party one I bought off ebay. Will that mess up the camera? Or should I have two batteries of the same kind?

Also, for someone who only takes the occasional portrait photos, is there a need for the grip? the problem for me is that I don't think I'll like the extra weight and also none of my camera bags will fit the 7D + grip attached. So that means that I must transport the grip separately and attach it when I use it (I am not planning on getting a bigger bag because my current bag is perfect for me..Lowepro Primus AW).

thanks.