Does opcache work under the suphp handler?
No, suphp is not compatible with opcache. You'd need to switch to a different PHP handler, like CGI with suexec, in order to use opcache. You can install those handlers through WHM -> EasyApache 4. More information on the different PHP handlers can how to install them can be found on our documentation below:
PHP Handlers | cPanel & WHM Docs
Manage PHP Handlers in Easyapache 4