Dwarves are not heroes?

[Groin Redbeard]

Originally Posted by Pitchwife

(The magic ring proved rather handy, too, but I can't remember whether the Dwarves knew about it and its properties when they arrived at the Mountain.)

Bilbo told Thorin about the Ring when the Dwarves were trapped in the Elf King's dungeons. So they knew that Bilbo was silent, invisible, and unfamiliar to Smaug. Though I think it all comes down to duty. Bilbo was hired to be a burglar and was going to be paid handsomely for it.

As has been stated before, the Dwarves took the trouble to procure a signed contract with Bilbo in order for him to be paid, but this also insures that he does his job.