They aren't children? I don't believe they are violating labor laws. The housing was probably arranged by the placement agency. The businesses are mostly exempt from minimum wage laws because of their size. I doubt that there's a relationship between the "rooming houses" and the shop owners. I think the reality is that (for example), if you want an ice cream parlor and coffee shop in Southwest Harbor -- instead of an empty storefront -- then you have to get service staff somewhere. How much more can you pay for a $4.00 cup of local coffee ;^).

As for hire local -- I don't know if locals can afford to work there for that short season.

There were other businesses that utilized local staff -- but they were mostly ones where the tips could actually support the staff. Some of the marinas had college kids interspersed with adults. In one marina in Maine, one of the managers of the fuel dock was lamenting that he used to work there "year-around" (they'd find something for him to do in the winter) -- now they hire him for the season -- then he's laid-off until, maybe, they hire him back the next late Spring. There were some college kids working there for the season. But I sense that they depended on the tips. That was a top-end marina. The kids all went to blue-chip schools and probably didn't really "need" the money. It was more of spending money thing for them. For the adult, it was the difference between something and nothing, but unemployment or moving out town to somewhere else.