I looked in the book’s index and Roe is only on 3 pages. I think you can assume most of him is either made up or is a “composite” of medics’ experiences. The main mention of him is in the Bastogne chapter:
Why would you assume that? He’s a real guy, and he died in 1998. His kids and grandkids created a web site about him and his experiences in WWII, and there’s pretty extensive information on all the other men in E company there, too.
Perhaps I overstated. Of course they could have done other research about him that isn’t in the book. I just thought the episode was designed to show a typical medic’s action instead of specificly Roe. Any speculation about him being a junkie based on the actions in the film have no relation to reality. The site you listed has a link from an historian. Link
It states that while the nurses were based on real people, it’s doubtful that Roe would have met them.