Should I inform ATC about minor deviations to maintain VFR while on practice instrument approaches?
Yes, definitely. Approach is expecting you to fly the approach as published and/or instructed and if you can't do that for any reason then you need to tell them. They may be providing separation between you and other aircraft, and if you start maneuvering without any explanation that could make things difficult for them. 

The last time it happened to me I was being vectored when my safety pilot told me that another aircraft was heading towards us. I turned and climbed and then told ATC "maneuvering for traffic, will resume 3000 and heading 150 when able". The controller acknowledged, waited until I was (more or less) back on course and then gave me another vector.

Having said all that, if you can't fly the approach without deviating all over the sky then you should consider if it's really worth it. First, because it may not be very useful or realistic practice, and second because if you put a higher workload on ATC then they may just drop you completely. The ATC orders 4-8-11 say:


  [...] ensure that neither VFR nor IFR practice approaches disrupt the flow
  of other arriving and departing IFR or VFR aircraft. Authorize,
  withdraw authorization, or refuse to authorize practice approaches as
  traffic conditions require.