Google/Adsense/Crawlers: I've never had issues with zbblock blocking the Google/Adsense crawlers and I use this now on two sites (one oxwall; one phpbb). Adsense would give an alert in their portal if their bots were being blocked from crawling.
If you need something whitelisted then search for their IP if the company posts it publicly and whitelist it..?
Gtmetrix issue: Yes, zbblock does tend to block those crawlers. With this plugin, you should be able to whitelist their individual IPs for their crawlers:
https://gtmetrix.com/locations.html
You may need to purge a couple of files first before whitelisting. If you whitelist and it still doesn't work then FTP into your server you can go to ow_plugins > botsblocker > classes > libs > zbblock > vault
you can purge both ipddbd.txt & ippbdb.csv
(which need to be purged regularly or they get to be pretty massive files over time, FYI)
Those two files will repopulate automatically, no big deal. It was designed to be flushed out regularly. I just wish the developer would create a simple button in the plugin screen so I don't have to FTP in for it, but it really isn't a big deal.