I heard that there was a strict, unwritten dmoz rule that only allows two listings per company. Is this true?
No, there is not a rule like that. The submitter's written guidelines do mention that no site has an inherent RIGHT to even one listing. (Certain kinds of sites are systematically excluded; and there's no category where even a relevant site is guaranteed a listing.)
And they DO say: "submit a SITE [only] to the ONE most appropriate category."
And they DO say: "don't submit mirror sites or doorway pages." Editors would probably call two sites about the same company "fraternal mirrors" or "vanity doorway domains" -- that is, either they contain the same information in a different format (and thus can't both be unique) or they contain different information from the same source about the same topic, and should logically be considered part of the same WEBSITE even though they have URLs containing different DOMAIN NAMES.
The EDITOR'S guidelines say "multiple listings and/or deeplinks are the EXCEPTION." There are, BTW, a few customary exceptions that have been mentioned in these forums. Aside from those, you as a submitter (or even as an editor working on a site with which you're affiliated) should not ask or hope for more than ONE listing.
And they DO say: "submit a SITE [only] to the ONE most appropriate category."
And they DO say: "don't submit mirror sites or doorway pages." Editors would probably call two sites about the same company "fraternal mirrors" or "vanity doorway domains" -- that is, either they contain the same information in a different format (and thus can't both be unique) or they contain different information from the same source about the same topic, and should logically be considered part of the same WEBSITE even though they have URLs containing different DOMAIN NAMES.
The EDITOR'S guidelines say "multiple listings and/or deeplinks are the EXCEPTION." There are, BTW, a few customary exceptions that have been mentioned in these forums. Aside from those, you as a submitter (or even as an editor working on a site with which you're affiliated) should not ask or hope for more than ONE listing.