Without knowing what year / model you are refering to it will be difficult for someone to give you an accurate answer, Mariner have used Yamaha and Tohatsu powerheads.
From my experience, yes. The engines are pretty well identical though I was told by an outboard dealer that the Yammy has a much better paint job!
I had a Mariner 2hp for 17 years before selling (still in good working order) and buying a Yamaha 2hp. All the spares so far have been directly interchangeable.
Some years of yamaha are not interchangeable with others in some areas.
Some mariners have some parts interchangeable with some yams, if there is the '3 tuning forks' logo on the block of a mariner, its yam based.