There are specific rules that outline when you have have a release available from the DOI.  Basic rule of thumb, shoot hand-held with no model and make no impact to park or grounds- & you should be ok. That said, you should review the rules for yourself and contact the park service if in doubt.

Agree with  most all the posts above, I hate the 15% commission rate, but as most of my sales are through partner sites- my returns are on par with SS & AS. Not knowing your portfolio or current sales dynamic... the best option maybe to upload a test port of 300 to 500 photos for a 6 month run. You are aready on the fence about it, give it a go and if you aren't happy... close your account and be done with it.  At least then you will know for certain.

It's to soon to give up, if you are having fun don't.  Everyone has to deal with rejections for reasons you don't agree with, slow months, and if you didn't start early on - not seeing a lot of sales before getting a solid portfolio with varied subjects.  As an added bonus, working on subjects out of your comfort zone will only make you better all around.

You have a day job and already said you enjoy the travel and photography, don't give up.  If you are enjoying yourself keep going.  One thing I had to do was evaluate what site's I was working with and pare down to the sites and subjects that were working. Realistically, you need about 6 - 12 months to look at everything and then decide. 

If you are traveling and want people in your photos, get a release app for your phone (I use Easy Release) and not have an issue with SS,IS, Alamy, or BS with the release it generates.  I never thought I would like or use it as much as I do.

Haven't had any acceptance issues from Alamy with a Fuji (XT-10 16mp) or Sony (A6000 24mp). Good glass for both mind you.

Even had trouble with FTP uploads once I was able to get to the contributor's page... sigh.  Just going to wait it out.