Cain has generally been quite submissive when meeting people and other dogs. I don't think it is anything to be too worried about because I think its his way to say hello. When he meets people, he rolls onto her back for a belly rub. When meeting other dogs he will bend to the ground and approach and than either roll on his back or sniff them. Depends on the dogs size. He's good at meeting dogs his size but quite a bit more submissive with larger dogs.
Is this anything to worry about or is it just the way he rolls?
It's not bad and much preferable to other possible behaviors. I think your dog's behaviors show lack of confidence in strange surroundings. More socialization is called for. It's important for YOU to act confident and show your dog that there is nothing to fear in that situation. Maybe I'm seeing more than is there because sniffing is a perfectly normal behavior. Rolling on back, not so much so. Work on building your dog's confidence.
Bill
http://www.skylarzack.com/rawfeeding.htm
Dogs are our link to paradise. They don't know evil or jealousy or discontent. To sit with a dog on a hillside on a glorious afternoon is to be back in Eden, where doing nothing was not boring-it was peace. - Milan Kundera
He sounds like a lovely dog. Having had a rather nervous dog who barked franticly at every other dog he met, I know how difficult it can be when a dog has bad manners. I don't think you have much to worry about.
I don't think there's anything wrong with Cain. He could just be a submissive dog.