I think choosing to only allow Hebrew writing will needlessly narrow the user base of what is already likely to be a niche site.
Ideally (in my opinion) there should be both the Hebrew spelling and an English transliteration. This will widen the user base, and invite more Google search traffic.
I realize this is unlikely to be followed by new users, so I suggest two things:
Users with the ability should keep their eye on the "review" queue, and edit in any Hebrew/English that might be required.
New users should be welcomed, (much as they are on Judaism.SE) and notified of this policy.
Other suggestions and policies would always be helpful.
As GMNoob suggests, one transliteration standard should be chosen and favored, but that doesn't mean others should be forbidden.