There are three legitimate ways to pay someone. An equity stake, payment by results, or the regular PAYE or trouser money.
When an actor or crew member takes a percentage of an indie film instead of a set fee, that is an equity stake. When a builder builds a wall and you give him money or you pay a sales rep a commission, that is payment by results. If you hire someone by the hour, the day, or for months at a time, that is regular employment.
Clarity in business is everything. If you are to get a cut of the company, i.e. an equity stake (or indeed any other arrangement) then now is the time to formalise that with a contract. The proposed arrangement as you have outlined it is not one I would recommend. It smells too much like pixie dust!