See this question: Can you peer review my database design for a school system?
I'm inclined to say yes, provided they have a complete design already and are asking for ways to improve it. If they are asking for how to do something, then its something for SO. That question you linked to looks perfectly applicable for this site (as far as we have defined the rules so far). If others disagree, I can be swayed either way as I have no strong opinion on it at the moment.
The rules of Code Review require real working code. We need to see the tables, columns, data types, keys, indexes, constraints — everything that one would need to instantiate the database. Additionally, we need to know the background information about what your application intends to accomplish. These are just the regular requirements for Code Review questions, applied to database schemas.
If you include all of that — as you have in your school system question — then you would have a fine Code Review question!
On the other hand, since our rules forbid requests to review pseudocode or unimplemented code, we can't review an entity-relationship diagram or anything sketchy that lacks the full information to instantiate the schema in a real database system.
I would say this is in the correct spirit of code review, provided the relevant schemas are provided in the question.