I'll mark Scottish and Irish surnames in the list with an S or I.
So let's start, in alphabetical order:

Frank Campbell Milne    S (well, of course!)
Alan Moran ??           I
Bob Edgeworth           I
Burt Gordon             S
Cliff Norman            S/I
Constance Mering ??     S (common in Scotland)
(only some heavily edited pieces by him?)
Douglas Ralston         S
Edwin Lester            S (Scottish variant of Lister)
Edythe Leslie           S
Ernest Leith            S
Gene Kerwin             S
Gladys Wilson           S
Gomez                   -
Harvey Maddon           S
(sometimes spelled as Madden)
Hayward Headden         (not sure)
(sometimes spelled as Headdon)
Herb Winslow            S
Jaysnoff Sisters        (variant of Jasnoff??)
Jeremy Lawrence
(common in Scotland but it's not where the name originates)
John Brooks             S
Lilian Jay              (common "short" surname)
Newell Chase ??         (in some rolls only?)
(name common in Scotland but is not where originates)
Noel Sherry             S
Paul Rickenbach ??      - (some Ampico rolls?)
Pauline Alpert *        -
Phil Ohman ??           -
(only some heavily edited pieces by him? Probably is Ohman himself)
Ralph Addison           S
Robert Farquhar         S
Robert Joyce            I
Ruth Ferguson           S
Sherry Brothers         S
Thompson Kerr           S
Victor Lane ??          S (After 1936 for some medley roll)
Walter Donaldson        -

But again, the style of many of the pieces is heavily influenced
by Milne's way of arranging, even though the pieces are credited to
famous and independent artists. I would love to give "audio" evidence
of this maybe in further text, if I can.

Also speaking of those pseudonyms, the style is often consistent in
the songs. This is not always true but pieces under the Harvey Maddon
name, for example, tend to use the same arranging methods, some
recurrent embellishments, phrases, tricks and cadence. Same goes for
other names, where the style is combined with the pseudonym used.

Even some pieces arranged by Freddie Rich and Muriel Pollock (who
were real persons of course), especially the former, those with low
catalog numbers (around 0400-0500 US listing, dated 1928-1929) have a
pleasant Aeolian flavor, but I won't include in Milne's pseudonyms.
It's important to not be fooled by the typical accented inner melody
at the tenor; it is not always a discriminating factor.

Another evidence could be that 60%-65% of the surnames listed above
are Scottish. Milne was from Dundee City, so these are the names he
might have heard in his home country and take in for the purpose of
pseudonyms; as well as the well-known pseudonyms derived from his
"family", such as Edgeworth, his wife's surname, etc. Some of them are
still English or Irish surnames so they could be the result of chance.
Many originate from Gaelic, Irish or archaic English.

* The question I would have liked to ask to Alpert would have been
just this: "How many rolls did you arrange and are credited to you?"

Too bad that until 1988, honestly not that far ago, no one asked her!
Many of her rolls however, are authentic to Alpert, and some of these,
while being part of pop music -- which was notoriously not hand played
but arranged on stencil masters -- are hand played, unquantized and
less edited. They allow to fully appreciate her authentic style.
See: Duo-Art 73908 (1930) Musical Comedy Tid-Bits from Broadway, less
strict in term of quantization and a very authentic performance.

I will conclude and also say that the way the Duo-Art dynamic was
encoded on the rolls sometimes is indicative of the eventual arranger,
or the editor, but I will stop here for now. I'd like to ask about
that later.

As I said at the beginning, I like comparisons and evidence, and I am
open to discussion, correction and addition! Thank you.

Best regards,
Luca Pastore