hi Oliver,
I don't think you can do it, unless you do some modifications on your own to have the library name not clashing.
When UI5 load "modules" (what is also referred as libraries) it also create a cache of "what modules are currently loaded" - and this is done using the library name, for instance, "sap.m".
As soon you Fiori Launchpad loads module "sap.m" (from sapui5) it sort of registers that already, and it won't (or shouldn't) load it again any other sap.m modules, in your case perhaps a specific version of openui5.
Worth mentioning, the "minVersion" does absolutely nothing, as you can see here openui5/Manifest.js at 9cad2b2cf6af9af074a4010dee416636a54a25d2 · SAP/openui5 · GitHub - so, you have a "dependency loader" based on a string and nothing else, which later would resolve into a requireJS module.
Unless you "rename" the ui5 libraries and make them available using the module structure (you would need to double check how it is handled in ABAP, I believe it could be slightly different from opeui5 code) you cannot use the "dependencies", because they are all taken.
You can however use the "resources" (manifest.json. sap.ui5.resources) and load the library just like the framework does for all other libraries, which you can find here: https://github.com/SAP/openui5/blob/9cad2b2cf6af9af074a4010dee416636a54a25d2/src/sap.ui.core/src/sap/ui/core/Manifest.js#L373
But once again, I think you will have "trouble" trying to run "sapui5 sap.m version A" and "openui5 sap.m version B" at the same time because ui5 does not load JS on the shim-shadow - reason why a "Component" in ui5 is not really a Component as one would expect it to be.
Hope this helps you somehow,
Dan.