Just want to make sure that I get the right info before I say for sure... 🙂
You indeed migrated the Windows machine off of the bootcamp partition to a standalone VM, and didn't just utilize Fusion to run the bootcamp partition in a VM correct?
If you definitely migrated it off, then yes, you can delete the partition as it's not used anymore. If you are running the partition from within Fusion and you delete it bad things will happen! Fusion will let you do either, hence the clarification.