You can, but the config might be a bit more difficult unless you are solid on how to cofig the two.
The stock MySQL install is pretty easy and you'll likely get better support as that's a very well known config for the support team. (They can speak to that better than I, but I know that it's far more common.
That said, we love MAMP for a lot of things (Approval-Q uses it to avoid conflicts with CatDV when running on the same machine.) And it's rock solid.
One of our sysadmins reports that it should be no issue but again, this is free advice off of the internet. (Worth every penny.)
MAMP defaults to port 8889 as opposed to 3306 but changing that in your CatDV Control Panel should get you connected.
On another realted note: I've not done the new install clean myself but one of our techs reports and we've verified from Squarebox support that the java MySQL connector no longer installs as part of the CatDV Server installer. So that will have to be manually installed into your lib folder in order to connect to MySQL after CatDV Server 6.8.
In our experience, 6.8 upgrades fine without this step, but it should be noted in case that changes, or if you do the "clean" upgrade where you wipe out your catDVServer folder in /usr/local/
I should report this in another thread, but I'm lazy and or busy. ;)