Hey @zotezo, thanks for your interest in Jetpack Boost!
No, you don’t need the main Jetpack plugin installed to use Jetpack Boost. The only thing you need is a (free) WordPress.com account to connect to.
I have run some tests with running Jetpack Boost and WP Rocket together, and haven’t found any significant issues.
Both plugins offer options to turn specific optimizations on and off, and some of the same optimizations are available in both plugins. I don’t recommend having the same optimization enabled in both plugins, as it is unlikely to benefit your site and may cause unexpected issues.
For example, I recommend against using Jetpack Boost’s “Defer Non-Essential Javascript” option at the same time as using WP Rocket’s “Delay JavaScript Execution” option.
WP Rocket also includes many customizable options, so there may be some combination of settings which can make it incompatible with Jetpack Boost.
If you find that any of Jetpack Boost’s optimizations cause problems on your site when run alongside WP Rocket, it should be safe to turn them off and return your site to its previous state.
Please let us know if you run into any trouble running Jetpack Boost, and we’ll do our best to help you out.