What is the difference between a gds built from openlane vs. a gds built from using caravel and openlane? Would a gds built from just openlane be compatible with the user project wrapper if it exports the correct pins?

You can easily generate a GDS using OpenLANE to integrate inside the

user_project_wrapper

. If you want to generate the wrapper itself, it's also possible but more complicated because you'd have to copy a whole bunch of the config, the pins, their position but also the whole power distribution grid setup etc ...

@Peter Sperrer: If you just "export the correct pins" you'll be routing them by hand. Which may be a big deal or a minor inconvenience, depending on the project size.