I'd only use it as a middle. I know an adult Pendragon who goes by Penn, and he still gets a lot of stick for his name.
Thanks for the opinions and suggestions everyone. I do think it would be a wonderful middle. I do have an association with Aspen, I knew one as a kid and she was a girl. I could never see it on a boy.
Personally, I think Pendragon is a bit 'out there', but if you like it, then why not? I think it would sound equally as handsome in the middle spot, and would go awfully well with other Arthurian sounding names. Here are some I think woud pair well with Pendragon:
I particularly like Aurelius Pendragon (It sounds so chivalrous!) :)
Uh pendragon ? your kid will get the NN Dragon.. Weird!!