It looks like
openssl-devel isn't an option. # Possible values: base, openssl, libressl, libressl-develDEFAULT_VERSIONS+= ssl=openssl-devel
Yes, I would suggest waiting for the dust to settle before blindly updating your production systems. If you want to try it then do so on a couple test systems. Did you set up a Poudriere repository? You could create a second repository with openssl-devel set as the default to see how things are going. That will allow you to test things without interfering with your 'production' repository.
True, just because it compiles and builds correctly doesn't mean it'll actually work. But if you set up a test repository you can test the resulting packages on a test system too. A lot of professional environments use DTAP cycles for this. Although you don't have a development cycle you can still follow the TAP part of it. You test your stuff on test systems (just making sure nothing breaks), then do acceptance tests (basically running tests with real-world data on a copy of your production system) before you put something out in production.