With the Viper’s Call node active in Swarmblade Form’s tree, I expected to attack faster with Armblade Slashes after spending points in Blood Flurry and/or Spear Flurry in Serpent Strike’s tree. This is not the case - the attack speed is unchanged.
Note that the bleed chance from the Blood Flurry node is carrying over to Armblade Slash, just not the attack speed.