Do you notice system lag when using Ventrillo by itself?
As I don't use Ventrillo (I personally prefer Mumble, Skype or Teamspeak myself) I cannot comment as to these two programs conflicting. However, system lag can be caused for a number of reasons. I recommend checking the amount of CPU and memory you are using when both these programs are running. If you have opened the music tab in Deepbot at any point the flash player in that could also be a contributor. If you aren't using that music player I would say to right click the video and press "Disable Player". If you are using the External chat function on Deepbot this can also put extra strain on the CPU.
Of course if you are using a beastly CPU like an i7 then ignore all of the above as the CPU would unlikely be the bottleneck.