He's a hard worker and he's loyal! Remember, Hufflepuff does not mean cuddley-wuddley little teddy bears. Hufflepuffs can be jerks just like Slytherins can be nice, Ravenclaws can be loud and annoying, and Gryffindors can suck at horror games.
Yeah, if you put it that way, I does make sense. I just thought, being sorted into a house is not only about your abilities and attributes, but also about what attributes you value the most. I don't know if loyalty and hard works are that much valued by Snotlout Going that way, he might as well be a Gryffindor or Slytherin, because they're about bravery and strengh of will and ambition and so on and so forth. Going by your interpretation, Astrid could be in Hufflepuff as well, right? She's clearly very loyal and always depicted as very hard working, even more than Snotlout is. (But yes, she's also very brave and strong-willed, which makes her equally well suited to Gryffindor).
But yeah ... you could put most of them into more than one house. Besides the Twins ... they're perfect for Slytherin I think. But Hiccup could as well be a Ravenclaw, 'cause he's very smart, creative and all that. Or he could be Slyhterin, because he's resourceful, clever and loyal to his friends. Or Hufflepuff too, because he's honest and fair and, like I said, loyal.
To stop my babbling ... it's really not so easy to say who belongs to which house. Even for the Sorting Hat is it not! So ... I guess, they're several right choices of Hogwarts House, are they?
Your take is certainly right. There's no such thing a wrong interpretation here.