....
I have it mounted separately so nothing is going to get written to it since grep is being executed from the boot disk, any temp files or output by grep will be written there.
What about that second part, about the encryption, is it all just unencrypted Berkerely DB prior to 2011? (I do not remember it that way, maybe I am confusing converting it from text to berkerely DB why I thought it was encrypted and mistaken about password encrypted - faulty memory)
Given this situation I also strongly suggest you take two dumps of each drive. Put them in separate storage locations, then put the original drives in a safe.
The dump files are much easier and safer to work with.
It's entirely possible that you try to retrieve the data, and fail. But a year later, a method occurs to you or is suggested, that is worth a try.
Have patience, don't give up, study and learn about data retrieval techniques.