Have the CVR work off the engine oil pressure is very old school.
Still the norm on the 737. You can switch it on manually on the ground and indeed quite a few guys do it to have the checklist recorded, however you have to remember to do that or put it into the the SOPs, it is not done automaticly. There is absolutely no legal requirement at least in the EU-OPS to have the CVR running during the preflight preparation.
Park brake is of course recorded on the QAR, via ACARS to the company and on the FDR. Quite enough recording of its status as it is, and on the 737 it has this huge red light plus the lever thingy to keep you posted about its status.