Casting Tablets remind me of all the media representations where naive protagonist reads an incantation out loud from an ancient book and magic suddenly happens.
I maybe predisposed towards Casting Tablets, even though Ars mechanics wise, few Magi have reason to make them.
However, do casting tablets predate the Order of Hermes?
Can a Seeker mage come across a casting tablet from the Order of Mercury, and since they have the Gift and a Latin skill, read the tablet and cast the magic even if they don't have Mercurian Magic.
Could some of the curses written on Egyptian tombs be the casting tablets for those curses?
One of the suggestions in Lands of the Nile for the various ancient Egyptian magical traditions is to adapt Learned Magicians. Vulnero charms as their "curse magic." I think that Learned Magicians can cast charms straight from a formulary without needing to learn it first, similar to a casting tablet.
So, the answer would seem to be "yes" -- except that you'd need someone whose Gift had been Opened to the Learned Arts, just like you need to be Opened to the Hermetic Arts to use Hermetic casting tablets. Mercurian magic may be different; the impression I get is that each ritual is essentially its own Ability/Art.
I must admit my internal vision of casting tablets is that anyone who has the Gift and can read the casting tablet can cast the magic.
But even presuming the Gift needs to be Opened to the correct Tradition, I would like to rule that Hermetic Magic owes so much to Mercurian Magic that a magus can "synchronise" sufficiently well with Mercurian Magic for such casting to work.
A casting tablet still needs ability in the arts. On the other hand an enchanted scroll that needs to be read as an activation trigger can work for most traditions that make magic items.