Yes. Whether it’s an non-“a2” passage for a pair of instruments, or a hymn-style staff for two voice-groups, separate stem direction is only an issue when the voices cross or when the rhythms are different. Otherwise, the two voices are shown as “chords” with a single stem, the stem direction determined by vertical position of the noteheads on the staff. (Yes, yes, I know there’s really no such thing as a two-note ‘chord,’ but you know what I mean!)
That was my primary complaint about every ‘solution’ ever offered by Sibelius for dealing with this issue. None of the proposed solutions ever came to grips with this issue in accord with established publishing practice. There were always ‘exceptions’ that had to be dealt with manually on an individual basis. (At least up to version 8, which I never used.)
Not being a Dorico owner/user yet, I don’t know how the new software is dealing (or will deal) with this point, but my hopes are high.
–LB