Hi Kelly, nice post and thanks for the tutorial !
I've been always thinking the same about resources from other games or at least from other UE-based games: if something is so cool I see no reason why not to use it also in UT99...yes, there some legal issues, I know, but, honestly, who cares in 2017 ? I think, after more than 17 years, people work only for fun and to give fun to an old community still "alive and kicking", as says a song by Simple Minds...oh years passed away so quickly ! (well, this is only my 2cent, I guess others can have different opinions about it...)
some time ago I installed Deus Ex GOTY and I found there some interesting animal assets (mice and seagulls)...why not ?