That's a REALLY good question. I just dug through the site on Wayback Machine and FTP server without finding that. I found GPL license file but it's not clear if it was just for the GNU tools or whole project. Also looks like a template they didn't fully fill in. Neither site nor DTOS paper referencing it mention a license.

Now, I know that many projects have used OSKit in open-source software and I haven't heard of a problem. I just found a license for it:

https://www.cs.utah.edu/flux/oskit/LICENSE

If you're doing a practice project, there's probably no harm in using Fluke work. You can always contact them if unsure. However, it seems like the work was intended to get out and be built on (definitely OSKit). Far as academia and industry types, this work has long been superceded by other tech and government contracts by those involved. I doubt they'd feel threatened.

Just my estimate on the situation. Never guarantees. Except for OSKit given its license.