I wouldn't think that would use any cellular data, as long as you're connected by Wi-Fi, but it should be simple enough to test. Turn on IPVanish and turn off data, and see if you can still browse normally.
I'm not familiar with the app, but have a general idea of what it does -- is there a noticable hit on throughput when using something like this?
I have not noticed any differences in overall performance, will try your suggestion of turning off the data and see what happens, will get back to you. Thanks much for the advice