Out of curiosity, I grepped x:\os2 for all 4 functions, nothing seems to use them. Or they're called by ordinal.
I also grepped \os2tk45. Found DosQueryPageUsage() only in os2386.lib, so a real function not prototyped. Also found DevHlp_OpenFile() in inc\devhlp.inc. Take a look at the inc for cardinal(?) and comment.
All but DevHlp_FileOpen are also in addendum.inf. I'd assume DevHlp_FileOpen is a typo with OpenFile reversed, a typo I could see making.