If you buy into EU, Doallyns story goes like this.

Doallyan was a beast hunter who Jabba hired to catch a Kyratt dragon for him. Somthing happened and the sarge. became somwhat of an indentured servant to Jabba. The helmet he wears is to add some sort of gas into the oxygan he breaths, and Jabba would only give him a days worth of this gas at a time.
When Jabbas death rolled around, Doallyan was still in the Palace. He and Yarna deGargan escaped the palace and went into the dune sea where Doallyan fights a Kyrat dragon and gets the jewels from its stomach. They eventually go to Mos Eisly.

This can all be found in Tales from Jabbas palace: Skin deep, the fat dancers tale