sounds like got a nice dog, hope he will fit in with your pack - no fun having dogs that don't get along. Make sure that your older dogs know that they are not being displaced by the newcomer - treat them with the status that is theirs, let Rocky know that he has not status in your house. He gets fed last, gets attention last, and so on. He isn't challenging you at seven months, just testing the water and trying to see what gets him attention.
Your dog is only worth 5,000 dollars because someone was willing to pay that amount for it - there is no intrinsic quality or lineage that he comes from that would make him worth several times the going price for well-bred working lines.
Did you not get papers with him? The only DNA test that you can do to my understanding, is one for parentage, and for that, he would have to be registered with AKC. So get his registration papers, post his pedigree, and there may be some experienced pedigree people here that could tell you more about him. Or just post his full registered name, he may have his pedigree available on-line.
The one thing I would suggest is to stop messing with him when he eats - great that he is easy going enough that you can poke and prod while he is eating, and get no reaction, so leave it at that. Constant interference during meals can create food aggression, instead of preventing it. Dog matures, has had enough of bone-headed owner hovering and taking food away, and bugging him on a daily basis, and will at one point let you know.
Leave him be, actually, when he eats, bring him extra treats and throw it in his bowy - this will condition him to having a positive association with you approaching and reaching towards him during meals.
Gryffon Vom Wildhaus
BH, OB1, TR1, AD
Rottweiler/Hairy Dog mix?? 2004-2015