Well, the prize is a $25 gift certificate to the ENWorld Store. If not wanting to support ENWorld is keeping people from registering an account, then I suspect that the contest prize will really turn them off — but even if it doesn't, changing up the contest rules to accommodate petty grudges against ENWorld seems like a bad idea. People nursing such grudges either need to let their grudge go and create an account or accept that ENWorld contests won't be open to them.
On the other hand, if somebody simply can't register on ENWorld, I agree that another option would be nice… although the only two things I can immediately think of that would actually prevent somebody from registering an ENWorld account are:
1) A lack of Internet access.
2) A previously banned IP address or account.
If the former, such an individual would also be prevented from participating in the contest, so taking steps to accommodate them seems like wasted effort. If the latter, as callous as this may seem, the inability to participate in an ENWorld contest seems like a fair penalty for anybody who abused their ENWorld account to such an extent that it to warranted the banning of their IP address or account (it does take either a lot of bad behavior or grossly inappropriate behavior to get banned from ENWorld). I hate the phrase 'tough luck' but I think that it applies here.