Yes, you can (assuming that the cached drive is a conventional 'spinner'). But you will probably not be able to remove the contents of the cache (unless the motherboard software allows it; I don't think that mine (Asus) does this).
To be honest, any form of caching is a security nightmare. I use SSDs as the system drives in both my desktop machines, and am very careful to store sensitive data on non-system drives, from which it can be more reliably erased. For this approach, I find that 120GB SSDs are quite adequate, and the price difference between those and the (maximum) 60GB drive you would use for caching is now quite small. That is why I have not used the caching facility on my newest motherboard.
While we are talking about SSDs, it is also worth repeating the basic advice that file and folder erasing is defeated by the wear levelling mechanism on the SSD, and so does not work, but that free space erasing, which fills the drive, does work.