I found the following on PADI's gear information
From those it would appear that PADI must be allowing Primary Donate.
To be perfectly clear:
PADI has 'allowed' primary donate for quite some time. It may not be the primary teaching approach that many instructors pursue, but there is
NOTHING in PADI standards, or Performance Requirements that precludes it.
Any Instructor who claims that primary donate is NOT allowed in PADI training is misinformed (or, worse, uninformed).
The training standards actually allow, as an alternate air source, use of a pony bottle. You DO NOT have to donate YOUR primary second stage, you DO NOT have to donate YOUR alternate second stage; you can donate a second stage from a pony bottle. I don't do that in OW (I DO use primary donate in my private OW classes), but it is perfectly acceptable.
Likewise, PADI allows passive donation of a second stage, PADI allows active donation of a second stage, although the emphasis, since revision of the OW program some 5 years ago, is on active donation.
Now, where some confusion may develop: many shops encourage standardization of training across instructors, which actually makes good sense. But, many Instructors, not unlike many divers, have no experience with primary donate. (And, these Instructors are not necessarily 'old farts' by any means.) They also have no experience with a long hose primary / bungeed necklace alternate regulator configuration, either, although that configuration is not essential for primary donate. As a consequence, those shops may elect to teach, as the standard approach to alternate air source use, the donation of an air source other than the donor's primary. Some shops may understandably be reluctant to move away from what many perceive to be a 'standard' regulator configuration: a 32 - 36" primary second stage hose, and a longer - 40" - alternate second stage hose. But, that set-up can be easily adapted to primary donate simply by using the (often, yellow) longer hose as the primary, and putting the shorter hose second stage on a bungee necklace.
It is always fascinating to see what is perceived as a PADI 'will allow' / 'won't allow' issue, but which is in reality an Instructor preference (or ability) issue, or a shop practice.