If two people go into an investment property business together - one as the investor and one as the property manager, is there a way for ownership to gradually be granted from the investor to the property manager in exchange for services until both have a 50/50 share in the property?
Sure. For an LLC this would often be done in the Operating Agreement through provisions regarding the gradual vesting or transfer of membership interests. But hire an attorney to prepare the paperwork -- a business attorney with real estate knowledge -- so it's clear exactly what happens if there is a breach of the agreement.
Nobody wants a partner who does nothing yet, due to an improperly structured arrangement, still ends up with equity.