The Donald Ross Society makes no mention of this being a Ross designed course. I did come across information that confirmed Ross Field Superintendent, Arthur Ham, being associated with the design of Knollwood (1925). Thus, the loose usage of the term "Ross inspired." Ham also designed Arbor Hills Golf Club in Jackson, MI (1925) and the Country Club of Jackson (1926). I could find no other architectural credits for him and it appears his work as an architect was very brief and limited to a few courses in Michigan.
Interestingly, Ross himself was doing a lot of work in the metro-Detroit area around the same time so perhaps these are courses he turned over to one of his junior associates or perhaps Art Ham left Donald Ross Associates briefly to try his hand at course design and wasn't successful attracting jobs and ultimately went back to work for DRA? He died in 1959. The fact he had no courses credited to him after 1926 is telling.
Chris Buie, a noted Donald Ross historian, could likely shed more light on Art Ham's role at DRA and his invovlement in the design of these courses than myself. What I can tell you having played the original Ham designed Country Club of Jackson 18 (Art Hills designed an additional nine hole course there in the 90's) is that it has a definite Ross feel and vibe to it. It's a really nice, underrated track and a legitimate "hidden gem" as few people know it exists. I've not played Knollwood and know little of it, but I know it doesn't receive the love and acclaim the elite clubs its surrounded by do, which isn't to say it isn't a fine course. It's always flied under the radar, much like the Country Club of Jackson.