When you go to get loans your rentals are counted and your rental income is not credited at 100%. All of your expenses are. So basically, unless you have some very strong cash flow, each additional home you get will reduce your ratios.
The seasoning you mentioned may also be considered.
HLS can chime in here to give more background on how lenders treat rental income and expenses for properties you own as you accumulate more of them.
hawk – can you query this person and ask him if he moves ownership of the properties around as he gets them, then does the cash out refi?