We've confirmed with our QA team that IIS8 DOES in fact work, but there are similar problems with IIS8 as there are commonly with IIS7. You'll need to go into the IIS logging configuration (in Logging, "Select Fields") and add fields that are de-selected by default but LEM uses to get key data like the hostname/source of the message. You definitely need to add the s-computername field which might be enough to resolve your error and get you moving, but you may need to add more fields to get the full range of data to show up.
I'm hoping we have this documented somewhere and if I find it, I'll be sure to have IIS 8 added to it and let you know where to find it.