The Gigrig is such a complicated thing it's hard to say.  There are plenty of people though using that with the H9 without any problems.  So, there's no fundamental problem with using the two together.  I don't know a lot about that product.  Does it allow you to keep a separate dry path and mix that with a signal going through a stompbox?  That would result in a phasey sounding signal…  Generally speaking with feedback, you'd want to check whether you've actually set up a feedback loop, no?