I've heard of Seafoam, but have never used it. I would personally recommend against using it, and only go with what the manual recommends - Techron every 7500 miles. Document when you put it in (or have the dealer do it), so you can prove that you did it if a warranty claim ever comes up.
If they figure out that you used something other than what is the service schedule calls for, then they could potentially deny a warranty claim.