First of all, yes, you need an unlocked bootloader. You can't flash custom kernels on a locked bootloader. Secondly, I've never tried that tutorial (I have a TX), but I'm assuming it should work fine, but, personally I'd either go with FXP, or one of the OMNI builds here in XDA, since, as far as I know, developers here have more fixes than what I've seen on FXP and/or CM.
Also, there are a easier ways to flash your ROM, since you already have a custom ROM. I don't think it's necessary to have to fastboot the kernel first.
Edit: The Carbon ROM I'm on also has a T version. The reason I'm on this ROM (and previously OMNI) was because FXP/CM roms have/had a battery drain that was never fixed, something that was fixed here on XDA.
Edit: There is this guide, it makes no mention of unlocking the bootloader so it might work?