Actually, sort of "no". They don't do any signing in.
A CM can get guests in via: complimentary tickets (and some CM's may get as few as only 4 one day hopper tickets per YEAR, given out in 2 batches of 2) or use the Main Entrance Pass. There are two levels of MEPs, those with a limited # of uses a year, and those with unlimited.
As the pp explained if the CM has a MEP they can usually get up to 3 guests the day they use it- the CM and the guests ALL have to enter the parks initially together at the same time. Keep in mind that MEPs have blockout dates, which are not in the same at all as AP blockout dates. They also don't release those dates for an entire year- (genearlly it's a few months ahead of time) so if you asked about say, a trip in November, the CM wouldn't know for sure yet what dates may be blocked.
Bottomline, while CMs do get *some* freebie tix, they don't get alot. And unless you know someone with the higher level MEPs, use the MEP entrance is going against their yearly allotment. Basically, be nice and appreciate of the CM who can get you in for free, because for most CMs it's not an unlimited benefit.
If you do get in with the CM's MEP- each person is given a 1 day hopper ticket at the turnstyle each day it's used, so yes, you can roam without them.
Good question how Hawaii will work. I PRESUME it is part of Parks & Resorts division of TWDC- and there are differences between bennies between WDW CM and DLR CMs and how all the discounts, etc work. I'd presume that the CM would get all the TWDC employee discounts which would be hotel discounts, the twice a year alotment of free tickets, and dining discounts. I have no idea if they would get a MEP or not, but I'd hedge on yes. In both WDW and DLR ... hotel employees are still part of Parks & Resorts and basically get the same types of discounts- depending on whether they are salaried/management or part-time (salaried gets a little better bennies etc).