Stripe doesn't care. You can open Stripe account and accept payments, you just risk deportation if INS finds out.
Your other options:
* offer the SaaS for free until you get Green Card. It's still valuable to find out if your product will be used when the cost is $0 and you can build SEO/reputation. If you don't want to paint yourself into a corner you can build a "lite" version, that withholds some features. When you're ready, you can add those features and charge for a pro plan
* you can setup a business in your own country (or some non-US country that allows easy formation of businesses) and have payments (Stripe) directed to that business. I'm not sure how INS would interpret such work-around, but it's a moot point since the probability of INS finding out in this scenario is close to 0%
* like the above but have a trusted family member to open and manage the business. It's still a work-around but almost certainly INS-proof