I ride packed dirt and gravel on a bike without shocks, is this trail doable on that kind of bike or do you need a proper mountain bike?

Yes but it's also easy to keep going and get lost if you go on to another trail I never found the trail that looks back to begining and it went from enjoyable to lost.

Most of it can be accessed on standard bikes but I'm not sure how enjoyable it would be. Definitely a mountain bike type of Trail