Doug,
Tom Paul and I looked at the original drawings for Flynn's redesign of Denver CC. If it was built as or nearly as drawn, it would have been a championship course with few peers. There were clearly influences from Pine Valley as he designed many segregated fairways and island greens within sandy wastes. The length of the holes and the demands intended were not for the average membership.
According to Chuck Bonniwell, a member who has done a great deal of research work at Denver CC, the course was simply too hard for the membership as designed by Flynn and only the general routing and 7 or 8 holes (with some of the difficulties designed by Flynn not incorporated) are all that were implemented from Flynn's 1922 plan.
Collis, perhaps Ross, and others did redesigns. After Spear Blvd was widened in the mid-50s, the course was further altered.
As far as Collis' other work, C+W states the following:
Harry J. Collis (1878-1937) was born in London and emigrated to America in late 1889 where he became greenkeeper at Indianapolis CC. In 1906 he moved to Chicago to work as pro-greenkeeper at Flossmoor CC. While there he remodeled the course into a popular tournament site, developed a turf cutter, and created a strain of bent grass named after the club.
After WWI, the work at Flossmoor resulted in other design work. He collaborated with his friend Jack Daray, professional at nearby Olympia Fields CC and operated a turf nursery.
He struggled with the depression and eventually lost his properties to bankers and the tax men. Flossmoor rehired him to be its greenkeeper but he died soon afterwards.
Course designs credited to him by C+W are:
Arizona: La Palma CC, Phoenix CC, San Marcos Hotel + C
Florida: Homosassa CC
Illinois: Cherry Hills CC, Dundee CC, Freeport CC, Harlem Hills CC, Indian Wood G+CC, Laramie CC, Navajo Fields CC, Normandy CC, Park Forest GC, Pistakee Hills CC, Richton Park GC
Indiana: Casa Del Mar CC, Longwood CC
Iowa: Newton CC
Maryland: Manor CC, US Naval Academy
Michigan: Chickaming GC, Walled Lake CC
Mississippi: Rainbow Bay GC
Courses remodelled include:
Colorado: Denver CC
Illinois: Flossmoor CC, Medinah No. #3
Michigan: Meadowbrook CC
Wisconsin: Rhinelander CC
As to his style, I have no idea whatsoever, perhaps those that recognize these clubs and know of his participation might shed some light on his design tendencies. If you or other members of Denver CC know what he did there, at Manor CC, and at the US Naval Academy I would appreciate some word on the subject as Flynn did design work at these courses too.