The AGMA list has not always been up to date so you may want to check if there are specific companies you have in mind. To my knowledge there is not another labor union that represents ballet companies like AGMA. I certainly could be wrong on that though. There are many companies that are not unionized. Some of those, however, do have contracts that are written almost exactly like an AGMA contract just without the union to back it. Those companies usually try to adhere close to AGMA so that their dancers don't want to unionize but are protected. They will be the companies who do good work but their budget cannot take the AGMA financial hit.
The issue with any contract is that you won't know until you see the wording of the contract how closely they adhere to AGMA guidelines and if there is anything written that tells you what to do if they don't.
DDs contracts have not been union ones. Both were very detailed, but one was more administrative friendly and the other more dancer friendly. A dancer friendly contract will read to show the protections it offers it's dancers while also giving the regulations the dancer must follow. Her first contract was very clearly written so that the company set the rules and the dancer was only protected as far as the administration wanted to take it. This showed up when individual dancers were given pass on some of the rules and others had to adhere. Or in the inability to ever ask questions about situations. The 2nd still gave the company ultimate control but showed how the dancer would be protected.
An example would be in her first contract: class was mandatory, the rehearsal schedule was emailed the night before (sometimes) and if the day went longer it just went longer. There was a dancer who was a company liason who was put in that position by the Administration. (not a dancer friendly contract) Total hours for the week were dependant on need.
An example in her 2nd contract: the dancer work week has a set number of hours. Class is mandatory with a few exceptions granted. If the company goes over those work week hours the dancer must be given time off. If, during theatre week, the hours are more than the set work week hours then the dancers must be given a day off to offset those hours. If the dancer goes over a certain amount of work hours at the request of the company, there must be additional compensation. Work hours not in the contract (with no pay) are optional. The dancers nominate/elect a company liason who is a dancer. They may speak to the administration on the dancers behalf but it is a dancer driven person.
Ultimately, in both cases the Administration has complete control over the dancer, but in one, there is more protection for the dancer than the other. This is the type of thing you will look for.