Has anyone had any luck running multiple webstores out of the same netsuite account?

Create an SSP application and copy the (source) SSP Application of your existing site.

separate web store licenses? not a problem. Same license, then it becomes tricky

We’re sharing items and customers, and multi-sites is enabled.

“multi-sites is enabled” - you mean you have separate licenses? Then no problems. SCS just enable theme/extensions you want for each domian. For SCA, same, but if you have extensions in the core that are not shared then you will need separate SSPs as @wbermudo said

No separate licenses, not even sure if multi-sites is relevant.

as long as you are ok with sharing everything that is setup at the website record level (price level, shipping method, payment method, catalog, subsidiary, etc) then you are ok

Thanks for confirming @Flo Meilan