Does Parallel still allow booting from a Bootcamp partition with HIgh Sierra? Will I be able to create a Bootcamp partition that I can boot into from Parallels once I've upgraded to High Sierra?
Yes, but there are a few issues. See Known issues with macOS 10.13 High Sierra and Parallels Desktop for Mac:


  Known issues
  
  
  Cannot create a new Boot Camp VM.   Fixed in version 13.1.0
  Cannot start an existing Boot Camp VM. Fixed in version 13.1.0
  Cannot install macOS High Sierra to a virtual machine with Apple File System type.  Fixed in version 13.1.0
  Cannot install Kaspersky Internet Security for Mac on macOS 10.13 High Sierra.  No workaround.
  Video artefacts when switching desktop spaces in Full Screen mode.  No workaround.
  A VM installed from Mac Recovery partition cannot upgrade to macOS High Sierra. No workaround.
  Parallels Tools system extensions are blocked in macOS High Sierra VM.  In macOS High Sierra VM open System Preferences > Security &amp;
  Privacy > General > click 'Allow'. See KB 124244
  Cannot deploy Parallels Desktop to Macs with macOS High Sierra (host OS).   See KB 124289