Not exactly sure what happened, since Soul Seeker's casting speed (the speed at which orbs are thrown out) used to be affected by attack speed, but now it is no longer affected (or at least, my experimenting has shown that it no longer is affected).
Soul Seeker @ Fast (5) with the 150 Hyper Skill active (100% recharge rate for 30 seconds) is giving me ~12-13 casts per 10 seconds. Decent Speed Infusion, Monster Park Extreme Green Potion and the Attack Speed buff from Dojo did not increase the number of casts that I counted. The amount of casts stayed consistent at Fast (4), Faster (3) and Fastest (2).
However, the increase in attack speed affects close to all of Angelic Buster's attacks (minus the rush skill and the keydown attack).
If anyone has a 150+ Angelic Buster and has nothing better to do, some further testing would be greatly appreciated.