(Depends if you are talking about architecture the skill, or architecture the genre)
generally any knowledge in an area helps with drawing said subject, although a lot of architecture skill knowledge will not be useful in art at all (generally speaking), so it's not worth studying architecture to get better at drawing.
but the architecture genre is essentially photos of buildings and building parts, which is exactly the sort of reference that will help you to create realistic looking pieces.
For photorealism/hyperrealism I can't help you there, but it takes a lot of time to add enough detail to make something look VERY realistic. You might not actually be aiming at that level of realism for a manga, so I don't think those terms are correct, unless you really are aiming that high of course.
The same technique could be applied to finding scenes from the real world (or video games) and drawing them in comic form - Big Ben and the Houses of Parliament, The Sydney Opera House, The Manhattan Skyline, a Temple near Kyoto etc. Just search a picture on google and draw using it as a reference. Then, for each, draw an original scene with a building in the style of the one you have copied - Gothic style, Modern curved style, Cityscape, Traditional Asian etc.
Yup I 100% agree. Building up skill takes time but if you always keep your goals in front of you then you can move towards them more effectively.
Hiroya Oku uses a 3d modelling program to produce the backgrounds (and also produce the character pose guidelines), so the software you choose will affect the art you can produce. It's essentially impossible timewise (let alone skillwise) to produce that level of quality by hand, especially in the timeframe of producing a manga.