I think theres some confusion here.
The ZAP Fuzzer is a manual tool which is separate from the 2 spiders and the active scanner.
ZAP is designed to be used with the permission of the target owner.
We recommend asking the target owner to remove firewalls or provide a test environment without firewalls and the like.
If thats not possible then you could implement an
httpsender script which replaces any strings that you think could cause problems.
I would also change the default ZAP user agent string :)
Cheers,
Simon