I'm curious if this is intended or a bug...

It appears when I restart Apache that all PHP pages begin to return
500 Errors / White pages. Only way to resolve this is to restart FPM
after restarting Apache each time. Is this how it should be?

I do not configure apache with PHP so they are not linked. The only
thing which links them is the FastCgiExternalServer command inside of
the Apache VirtualHost configuration. But if FPM is already running
and Apache is restarted, it should automagically reconnect to the FPM
process.