On combo releases you profile whichever version is being marketed as the Primary version Blu-ray if it is a Blu-ray + DVD or DVD if it is a DVD + Blu-ray.  Only the features, video format, audio tracks and subtitles are profiled for the Primary version being sold.  Any of the features, video format, audio tracks and subtitles will be profiled under a separate profile for the bonus DVD or Blu-ray.

On the disc formats you would check both Blu-ray and DVD.

Under Disc ID info you would all the Disc IDs included in the package and they would both be considered Main Feature.  One would be "Main Feature (BD)" and one would be "Main Feature (DVD)" if they also include a digital copy then you would add the disc ID as "Digital Copy" as well.  If there is a Special features disc included it will be listed as "Bonus Materials".

Which ever version of the movie is considered a bonus Movie in the case of a Blu-ray + DVD the DVD version would be the Bonus Feature Film and you can add that disc under Box Set Contents following the Bonus Feature Film rules.

Solely depends on the marketing however, Blu-ray + DVD combos as well as DVD + Blu-ray combos are becoming more common.  Some will even include a Digital Copy of the movie.