Yes, that's my understanding as well while reading the manual (please all read the manual!)
And I think I can add the following:
The requirement that you can use a speaker of a PRIR in different (as in Dolby, DTS-X etc.) rooms is that the speaker label is available in all those rooms. See the table on p. 95ff.
There you can see that DTSX can have all the labels that Dolby Atmos has (e.g. Ltf - Left top front) but DTS-X can have additional speakers with labels that Atmos don't support, e.g. Lh - Left height or Lhs - Left height side. If you labelled a speaker as Lhs while creating a PRIR you can't use this speaker in an Atmos room, even if the position of the speaker would be correct for Atmos (but then it would have been labelled wrong by the user).
For a correct Atmos setup, up to 9.1.6, all speakers, if labelled correctly, can be used in Atmos and DTS-X (and PCM) rooms.
So the labelling of the speaker before creating a PRIR is a crucial point!
What I still don't get are the angular position requirements of the setups.
If you look at the table on p. 95 ff. there are azimuth and elevation angles mentioned for each speaker (which are sometimes odd), in the Notes it says:
The azimuth and elevation angles are default values–
the angles can be changed to match a physical loudspeaker layoutduring a PRIR measurement.
But I think, and this also mentioned in the manual, that these angles are just for info and are not used in any processing - at least not in the SVS processing.
The decoder assume specific angles and no one knows these at the moment (maybe even not the Smyths. Maybe MDS, the board manufacturer? Are there whitepapers or spec sheets?)