I believe there are two different levels of ground instructor. There are the low time, younger entry level. They do basic indoc, and the initial device training. If there are not enough students, they get farmed off to HQ to work on projects.

Then there are the older more experienced Senior ground instructors. They can do the same stuff as the entry level, BI, device training, but also typically do recurrent ground school. I think they are the ones doing recurrent gs in DFW and LAS, maybe as local hires?

I'm sure there is a basic contract, but if you have more experience, you might be able to negotiate. There is at least one recent ground instructor who brought a lot of 121 sim experience who made it to the line in less than two years, but not the norm.

Seniority is based on being hired as a pilot. As a ground instructor you will go through training and get typed.

The program has been around long enough that there are now former ground instructors who are now line captains working as sim instructors.