Can I ask, what 'type' of viruses should be handled that way?.
You can do it that way with most "standalone" malware like Trojans, Backdoors or worms. But you have tofind out first if it doesn´t modify "dangerouse" things in the registry, like "shell open commands" for exefiles.
what does it mean on that link site when some of the entries are marked 'undetected' by Adwil. Is this when it's a generic virus?.
No, that means that Avast just not find these viruses( Vgrep update 08/2003!). Generic in this context mean, that some AV-Firms choose a signature that will match with more variants of that virus. It covers more Variants with only one signature. So it is able to tell you that the file is infected, but not which Variant it is.