As I have discussed earlier, culture is an inseparable part of a company. This is something important to take in count when recruiting. Just looking at numbers and hoping it will work out is not enough. You will have to make sure the prospect fits the organization. But how do you test for this cultural fit?
Valve has made its culture partly visible in a form of an employee handbook. By making these things explicit you will make it easier for people to evaluate whether they would like to work in the sort of environment you have in place. This is only part of the story, though.
Rather than hiring through a proxy, let it be a hiring manager or a HR agency, ask the people the person would be working with. In case you feel good about the person and want to play it safe, you can consider implementing a trial period. This is something Buffer has done with great success.
By actually working for a period of time together both parties will have a good idea if it's something to keep on continuing. Alternatively you could employ the person through a freelance contract and work towards something more permanent as trust is gained. Sometimes retaining the situation as is might actually be preferable to employment. Flexibility can be a good thing.
I feel this is one of those things you should tackle early on. If there's no fit, things can get awkward over longer term. It also restricts the potential of the arrangement. Good environment can bring the best out of people while inverse is true as well.