Can I use WP Rocket with SG Optimizer?

Yes! WP Rocket is compatible with all 3 levels of SiteGround’s caching:

• Static Cache
• Dynamic Cache (NGINX)
• Memcached

As of SG Optimizer 4.0.5 and WP Rocket  3.0.4, when Siteground's Dynamic Cache is active, WP Rocket's  page caching will also be active. In these cases WP Rocket's page cache acts as a fallback in case a request isn't served from Siteground's cache. 

When you purge the WP Rocket cache it also purges your SiteGround cache, and vice versa.