It will work just fine ..... but is there a chance you have AC power nearby? if so put in a small switch.
As long as it's 6 and not 6a, and given the length of the run, they shouldn't expect to run 10G, this would work. But I really don't like placing hidden active equipment in a path. It also prevents them from using anything but Ethernet on this run.
If, as Hal mentions, they're just going to run 100Base-TX or T4 over it, sure, it'll work fine. It will probably work fine for Gig as well.
But, it all depends on their use case, and whether or not they're asking for certification on these runs. It's worth being cautious here.
