i don't think hellsing was put on adult swim, i think G4TTV took the rights and put it on their short-lived anime show. they had some good stuff, did a midnight run sort of thing for a while, but then petered out when they didn't get enough people watching. replaced it with the Midnight Spank.

ahem. some good shows that made it on G4 but never got props:

hellsing (pretty sure)
RahXephon
Crest Of The Stars
Banner Of The Stars
uh......
Betterman?
yea. Betterman made it on there.
lessee.......
.....
....i think thats it. they reran CotS and BotS a couple times, and squeaked RahXephon in at the end, and thats about when they got overshadowed by adult swim and the Anime Network, for those who have premium channels (you bastards, you get excel saga on TV )