Re: Is it ok/possible to install 'oneiric' PPA pkgs on Natty?
TBH, I'm not sure, but I think it would be a bad idea. that PPA will likely have 11.10 versions of your core software and configs, so it will upgrade your existing files accordingly.
if you have a PPA for an individual app (say mplayer or vlc) then I wouldn't be that worried about it, but that looks like the entire system root. make sure you have backups before experimenting.
Things are rarely just crazy enough to work, but they're frequently just crazy enough to fail hilariously.