Will macOS High Sierra support my iMac's 500 GB SATA internal physical drive?
Yes, while APFS is optimized for SSDs you can still use it for HDDs as well.

Installing macOS High Sierra on a HDD installation of macOS Sierra won't prompt you to convert it to APFS, though.

See this quote from Apple.com:


  Can I use Apple File System with my existing hard disk drive?
  
  Yes. Apple File System is optimized for Flash/SSD storage, but can
  also be used with traditional hard disk drives (HDD) and external,
  direct-attached storage.