the way I was told to set mine up .. the boiler pump will run all the time... and the house circulator ( I am heating 2 houses) will be intermittent... so my guess is that the check valve need to be after the house circulator.
Dunno about other mfr., but CB sez put checks in the returns, at the boiler...I would put them on supply/return both...or skip the checks and use Taco IFC circs, they have a check built in.