EOS lenses support autofocus and iris control from the camera body, FD lenses generally do not (late examples had a form of auto-focus and an aperture ring that could be controlled from the camera body, but this was through a mechanical linkage rather than through an electronic aperture diaphragm as on the EOS lenses.
NB the correct name for the EOS lens mount is the EF mount.
I had a look at the red rock system, hmmm, It's a lot of money to spend on an adaptor and rails. On top of this you would have the cost of the lenses, and you would want faster (i.e. brighter more expensive lenses) if you opt for FD lenses then you are buying lenses with 30 year old plus designs, i.e. designed for film, not CCDs, you risk vignetting and colour fringing.
Even the very newest FD lenses will be 20 years old, so thats a lot of dust to build up, the risk of mould, leaky diaphragms....
Nikon AF-D lenses may well be a better bet.
Going by the kit I saw, it's to fit a 72mm diameter? so thats going to be a Canon XL or Sony z1?
You are going to shoot through the exsisting lens, through their own adapter lens (required to adjust back focus onto the front element of your exsisting camcorder lens) and then through a 20 year old film lens.
Wouldn't be me.
If its a canon XL series you use, buy canons own adapter.
Its a lot cheaper a lot lighter and more portable, retains aperture control and gives you the choice of using much better lenses, many of which are designed for use with digital sensors...
Going to all this expense for a camera that records at 8 bit colour compression......
If you really need this kit for a job, then hire in the right thing and put this in the budget, this all seems like a bodge, if its for personal use well, good luck.
On that note the EF mount and the FD mount, although both being of the bayonet lock type, have different bayonet patterns.
The FD mount has been discontinued since the launch of the EOS system in 1988, so I doubt that is the system you want to use.
EOS EF mount lenses can be used on the XL series of camcorder via an XL to EF mount adapter which canon make.
Do take heed that because the XL cameras use 1/3rd" ccds they are around a seventh of the size of a frame of 35mm film (that EF lenses were designed to cover) therefor a 50mm lens on a stills camera will behave more like a 350mm lens on an XL type camera. Great for extreme close ups, not great for wide angle.
Also there was only ever one canon EF lens which featured a power zoom (an optically cheap 35-80mm) and even then i can't see a way to control this from a camcorder body, so if you want to attach a zoom lens then you are looking at manual zooming.
Unless you have a very expensive HD camera with much bigger CCD's than the XL series you are going to have to take account of this magnificiation factor.
I have to confess i don't know a thing about the red rock kit, but at least know you should have a bit more of an awareness about the important differences between canon EF mount and FD mount lenses.