The company in charge of animation production for O-Yui is
T.N.K....and last time I checked, I don't think m.o.e. worked on
Licensed by Royal. Or dabbled in shounen-ai OVAs/drama CDs like
Papa to KISS IN THE DARK, for that matter.
Although the majority of works listed on T.N.K.'s site is indeed of the bishoujo-moe persuasion, so I won't blame anyone from making the assumption that O-Yui was done by m.o.e....
Edited to add a link to
m.o.e.'s official Web site - which does not list O-Yui as one of their produced works.