sticking brake calipers would certainly decrease MPG.

I have never used Seafoam, but I do use Subaru's Upper engine cleaner can - Fuel System - Carbon Maintenance | Subaru Genuine Parts

It did a hell of a job on all my cars! By the sounds of it, its the same as sea foam, removes all the carbon deposits on the valves and in the cylinders. I used to take off each spark plug and spray into each cylinder, then I know its in each cylinder (don't do this when the engine is running.) Then I spray the rest into the manifold.

I can't help you with the question as to if its recommended, but its generally pretty safe.