The Digital logo does not use any known font because it was hand drawn
by a graphic artist. It looks very similar to the Helvetica/Univers
"Swiss" type fonts but is not identical to any of them. As someone else
has noted there is a PostScript version of the logo. IIRC it was
produced by digitising a large film master which revealed some
interesting things - for example, the two i characters aren't
identical. For producing print copy before the age of PostScript
Digital used dry transfer sheets that were custom made in a variety of
sizes.
I'm afraid that I cannot help on the other font(s) used in the pdp logos
and on cabinet panels.
jb - London, UK