Firstly a note. Data Element of type URL Parameter internally uses _satellite.getQueryParam() and _satellite.getQueryParamCaseInsensitive() to look for query parameters. They are "not safe" to use because they aren't officially listed in the documentation for public use. Technically Adobe could make changes to them in the future that may break your code if you use them, and that's on you.
Having said that... code for getting URL parameters are extremely common and straight forward, and in practice, it is unlikely Adobe will ever change them. On top of that, I have heard Adobe has stated that, while they will continue to support DTM in the foreseeable future, they have no intention of doing any more major development on DTM outside of fixing critical bugs if found, in favor of working on Launch.
So, between those two things.. in practice, it's probably okay for you to use them without risk of them getting changed in the future. But if you want to be super safe about it, then follow the link I posted above and put your own function in DTM to use.