I totally understand about keeping files local as well as on the Dropbox servers. Fortunately, that behavior is the default in Dropbox. Unfortunately, the default for OneDrive is the exact opposite. By default OneDrive keeps no files locally and instead keeps all files only on the OneDrive servers. I recommend strongly not to use OneDrive unless you change the option.
That being said, keeping your RM database within the Dropbox folder actually is quite dangerous. There are two kinds of people who keep their RM database within the Dropbox folder - those who have already been bitten by data corruption and those who will be bitten by data corruption. Notwithstanding your experience so far, the risk is quite high.
You can mitigate or really eliminate the risk if you are willing to pause Dropbox before starting RM and to resume Dropbox after closing down RM. I worked that way for many years with nary a glitch.
Even if you do luck out and never have any data corruption in your RM database because of Dropbox, be aware that Dropbox is very aggressive about backing up your RM database to the cloud every single time you make a change to your RM database. Even something so minor as highlighting a different person can cause your RM database to be changed, thereby triggering a Dropbox backup of your database. This can result in excessive network activity and poor performance of your machine.