Me again

with yet another question lol
Sam has started displaying a rather odd behaviour which I'm not sure whether I should stop or not?
It only happens with my toddler Gregory, who spends 50% of his day laying on the floor playing or watching TV. Sam will go and very purposefully stand over him very still, Greg then crawls between his back legs and Sam will re-adjust his position to be over him again???? this "game" will continue until I stop it because Greg is getting frustrated by it (usually because Sam is in the way and Greg wants to be on the floor) or until Greg gets bored and stands up or goes and sits on the sofa.
My mum thinks it's a dominance thing and it should not be allowed at all, but I wondered what you all thought, I should add that sometimes my son begins the game and gets under Sam on purpose.
So does this sound like just a 'game' or should I be stopping it?
Thanks
Sally and Sam