Perhaps turn the question around the other way … does the UBports project list the Librem 5 as supported hardware? https://ubports.com/en/supported-products
Another question would be, regardless of whether it is supported or whether it works: has anyone tried it?
If you yourself intend to go down this road, I would try putting it on a spare uSD card and booting from uSD card (requires up-to-date uboot). That way, if UBports is epic fail on the Librem 5, you didn’t mess anything up.