Yes, SD/MMC cards have controllers that do wear leveling. If they didn't, you could destroy one in a matter of minutes with the wrong write patterns.
That's actually a problem for some embedded projects. There's absolutely no way (apparently) to know what sectors might be wear leveled at any time, so a power cycle at the wrong time can destroy data anywhere on the card, no matter where you THINK you're writing. (don't ask how I know :) )
SD cards must be used with a system that guarantees a clean system shutdown (or at least that writes are allowed to complete), or data loss will (eventually) result.
The problem is that the wear leveling process is entirely hidden. ANY sector on the disk could be moved at any time (swapped with the page written), and if power was to fail in the middle of that process that random sector could get corrupted.
While there ARE reasonably safe ways to implement this move, it's not in any spec so you can't trust that the card will do it. You could test one card, have it work, then the manufacturer could change the implementation without changing the part number and you're screwed.
From testing, my SD cards' controller does NOT do this in a safe manner at all.
I may look into a "high reliability" SD card I saw advertised specifically for power failure tolerance... but then you have to trust the manufacturer to do that correctly, and I don't. I really want direct control over page erases. I'm still trying to figure this one out.