This screenshot was taken with 3 truly superb gold glyphs on my jewelry, that increase potion effect duration by 3,6s each and 3 points in snakeblood. The effects don't change from the screen posted before. I also checked a potion, instead of a poison and for that, the effect of the glyphs was already visible in the crafting window.
Unfortunately I don't know which set you mean with "assassin set", so that set's effects are missing here. But I think it's safe to say that neither glyphs nor snakeblood affect alchemical poisons. And btw. snakeblood does the same as always, it just decreases the duration of negative potion effects by 100% (at 3 points).