I believe no. On the gamecube, the component cable had eletronics in the cable to do signal conversion. With the Wii, the component cables are just cables, all the signal work is done inside the system, rather than in the cable like with the Cube.
Plus, the connector has changed. I have the component cables for both and they aren't interchangable. I was disappointed at first, but at least I was able to get Wii component cables for $13 shipped as opposed to the Gamecube ones which were $35.
i have both as well and have modified my gamecube component cables and hacked components for the wii too. i can tell you that they are nowhere near the same thing. i just checked ebay and it seems that they gamecube component are going for around $50 now.
Last time I was in EB Games, on a whim, I asked the guy if they had used component cables for the Gamecube. I think people are turning them in with the $50 credit towards the Wii thing. I scored them for $5 bucks! I should have asked if they had more, I could have made some quick $$ on ebay.
If people knew how much they're worth now, they could've got the $50 for the cube and sold the component's on ebay for $30-$60 and ended up with almost $100 off on the Wii.