I have an old Promaster FTD 5600 flash. These flashes have an interchangeable module that allows it to work with different manufacturers' TTL systems. Right now the flash has a Nikon module; it does work on my Canon T3i/600D, but only in manual mode. I'd ideally like to be able to use it with TTL on my Canon. I therefore have two questions:
The dedicated foot may or may not work properly with a newer camera of the same brand. Your best bet would be to get a non-dedicated version, if available for your make and model, and then use that. There are a couple of caveats, though: one is, the flash unit must have its own eye, or it will only fire at full power. If the flash is completely TTL-dependent, it won't be usable in the manner I've suggested. The other caveat is trigger voltage: it has to be pretty low to keep from frying your camera.
You can look up trigger voltages on this site: http://www.botzilla.com/photo/strobeVolts.html.
I just checked and you Promaster 5600 is not listed, but several other promasters in the 5000 series are listed as having very low voltages, quite safe even for Canon, which is the pickiest.
I just tracked down a pic of the 5600 and it looks like it's TTL only, so it looks like you're out of luck. The module is still worth a try, it won't wreck anything, but it may or may not work as you would like it to.
Whatever you do, do NOT use a foot for a different brand of camera than your own.