Is there anything particularly beneficial about the Dallas Stars hosting the 2018 NHL Draft?

Their fans get the chance to attend the draft (been to a few- most recently in 2016 when I made the trek to Buffalo to see Auston Matthews get picked first overall and piss off a bunch of Sabres fans (salty as ever every time Leafs fans invade their arena)) in person which is nice.

Revenues generated don't alter their salary cap; the cap is set by the league and each team has the same cap so it wouldn't help Dallas specifically. The city gets the benefit of having 30 other teams in town (helping hotels, restaurants, bars, transportation companies, etc) plus they become the main focus of the hockey world for a few days, and their fans get a chance to (hopefully for them) see the next great Dallas Star player get picked.

The event is a league event, as it were.

Salary Caps aren't based on a single team's revenue so even IF they get all the money from concessions etc. it won't "buy" them any more salary cap space. The salary cap is set by adding up all the HRR (hockey-related-revenue) from ALL the teams in the league and then applying a rather complex set of mathematical formulas to establish a cap. This cap is the same for everyone no matter how much individual teams earn.

-Teams can't "buy" draft picks. Teams are awarded draft picks based on how they finished in the standings the season before OR they can trade for draft picks (by trading players or , for example trading an early (first round) draft pick for 2 or more picks in a lower draft round.

so all them cowboys can attend a draft for once. and not the ones up in calgary

Exposure.