No, hashing passwords is a different case because you know what the user is so you can use a unique salt. The password itself is also high entropy. For this use cause you can have at best per-post salt.

Think about it. The task that you are asking for is to quickly check if a user has voted for a post to prevent duplicates. So literally the operation you want is the same as you are trying to prevent. If you can enumerate users then you an by definition check if they have voted for a post.