There's no such thing as allowing on steem as it is a decentalized platform and everyone can do whatever they want. The reason we are downvoting the bidbot users is to discourage the vote buying behaviour. Everything is allowed, no one is prohibiting you the use of bidbots, but if you do, some other people can vote or downvote your content. As I said, there's a lot of manual curators out there looking for good content to reward, there's no need to buy votes if you create good content.