Two issues: first, this library isn't part of the standard Java or Groovy environment, so you'd need a way to make it available. But second, and more importantly, Hubitat has an allowlist of classes allowed to be imported in the "sandbox" that user apps and drivers run in, there would be no way to get this--or anything not otherwise allowed--into that in there in the first place, at least not without staff doing it (unlikely for third-party libraries they or the system doesn't have a use for, but they have been known to listen to reasonable requests).
What you can do in the meantime: in the event that you're able to re-implement the pieces of this library that you need in "plain" Groovy and Hubitat's allowed classes (and the extras provided by the app and driver environment), you could re-implement what you need. Probably hard, maybe impossible, but I don't know details if the iCalendar specs. You could also run this on an external system via whatever means you want--making it act as a "middleman"--then find some way to integrate it into Hubitat, like MakerAPI or a custom app/driver. You may also wish to see if someone else has already done something similar before, either here or in the similar "classic"/Groovy SmartThings environment, with which Hubitat's is largely compatible.