Just to be clear here, shaunjurr is correct in his understanding.
Whilst I appreciate information regarding server defrag, my original post was actually regarding "application defrag" the such of which occurs when Exchange runs a storage group database defrag. This is an Exchange function, and completely different to what the likes of Diskkeeper is doing.
And also to be clear, I believe running Windows disk defrag programs such as the built-in one provided in Windows - or Diskkeeper - is an extremely big no-no when using a VMware/NetApp infrastructure.
Thanks for the help so far shaunjurr. And as a follow-up, I have since ran some "reallocations" on some of my highly used vols and it seems to work without issues. It also reported some of my vols as being extremely fragments (rating 9). Therefore I am starting to schedule reallocate - especially after my Exchange defrag takes place. So far so good.
My eyes have been opened to the world of reallocate and its importance!