Well I decided to do some test of certain things and weapons because I have nothing better to do with my time. Turns out the poison resistance actually works, both with R attacks and with normal skills when your opponent is using a weapon with poison on it.
166/135 with arrow shower 393.5/352 with shadow shot
arrow shower was tested with 12 different arrow damages and the shadow shot with 4.
Just thought some people would like to know.
Testing was done with a scorpian scythe +6 which has 10 less resistance to poison so the differences would have been more with a chitin bow.