Slingerland did make a few "private label" drums, but they typically had the Slingerland name on them. If you check out DrCJW's badge page HERE, you can see a few of them.
What I find most interesting on that DrCJW page is the first Slingerland badge. I've attached it alongside a Eugene Geisler badge. Look similar? But as mentioned above, Slingerland didn't start making drums until a few years after 1925. (1927 according to Wikipedia, with the first Slingerland-branded kit available in 1928.) Is it possible your 1925 date is off by a few years?
Geisler as a company definitely pre-dates Slingerland. They apparently made drum heads, according to this page from a 1917 issue of the Music Trade Review.
I also found a few more pics of a Geisler snare drum on this page. The tensioning system sure looks like it was made by a banjo company. And in a case of "what's old is new again"... Ever see a Legato marching snare? (Legato was an Australian outfit that was bought out by Remo.) Their tensioning system was also inspired by banjos and I can see some similarities to the 1920's Slingerland design.