Hitachi drives are currently being sold as HGST drives, which is now a division of Western Digital.
I'm unfamiliar with the issue iFixit notes with 2009-2010 iMacs, and I wish the product pages had a description of the issue (replace drives with same brand as original or else! ), or at least a link to an explanation. It's possible that different drive manufacturers used different connectors for the thermal sensors, and iFixit is trying to ensure that you don't buy a replacement drive that won't fit your current sensor cable. As iFixit doesn't stock drive sensor cables for aluminum iMacs at all, they may just be trying to prevent further trouble.
This eBay search brings up a variety of different sensor cables; only one retailer is specifying the drive brands to which they connect. To my eye, one connector on each of the cables looks identical, while there appear to be small variations in the others. In the closeup photos, the connectors look like they attach to the jumper blocks.
One solution would be to buy an HGST drive that fits your requirements, and see if your current sensor cable fits. Another solution would be to pick the drive you prefer, regardless of who makes it, and then find a sensor cable that fits. My theory is that Apple uses only one connector for the logic board, and uses a matching cable to whatever drive happens to get installed.
It is annoying, though. This is really something the manufacturers should have standardized. I'd really like to see iFixit's product pages explaining why you need to do this.