absolutely yes, PHP has to do with application server handled by your hardware so OpCache will be ONE for anything making use of it, be it wordpress, moodle or anything on same server, making changes in OpCache for one application (e.g. moodle) will reflect for every other application, like default value for memory allocation is 256MB where a larger moodle site requires say 512MB or 1GB or memory allocation, wordpress will be allocated same amount of memory for using OpCache, but if you are running multiple instances of moodle then the value of memory allocation MUST be increased to cater the needs of all moodle instances.
Unless, you can setup PHP individually for every application, which I am not aware possible in Linux, but in Windows server environment, yes.