You know how sometimes when you are downloading files from a server you are connecting too, and often the file is finished before the percent complete reaches a 100%? Well, these are actually compressed files. When Unreal downloads these files, it first stores them uncompressed in the UNREAL root directory (\UnrealTournament) as cachexxxxx.tmp, then when the download is complete it uncompresses them to the cache directory. BUT... it doesn't delete the original tempory files, leaving them stuck in the UnrealTournament directory.
So yes, they are SAFE to delete... All of them.