This may be a really dumb question, but is the kernel part of the ROM itself? In other words, if I don't like this and want to switch back to my old ROM and stock kernel, do I just need to reflash the ROM? Or will I have to do something special to backup the stock kernel?
Not a dumb question at all. Some ROMs include a custom kernel while others do not. The thread that has information about the ROM should tell you whether a custom kernel is included or not. Barring that, crack open the zip file the ROM comes in and look and see if it includes a boot.img file. If it does, that it also includes a custom kernel.
Boot.img contains the kernel and other important start up files
System.img contains the applications and drivers.
While this ROM as is does contain the kernel, you could easily strip it out if you wanted using a rom kitchen. Conversely, you could put this kernel in with the stock rom (and have the keymapping issue)..
Basically, if you did a nandroid backup before flashing a new rom, or downloaded a stock backup from somewhere which includes both the boot.img and system.img, you can always get back to stock. Just restore the backup and both the kernel and rom will be back to stock.