This is probably a rudimentary question but if I am in any mode, say A# Dorian, am I free to use any chord progression on the scale? For example could I use a Diminished chord progression on the Dorian scale, or are we limited to specific progressions for each mode?
First of all, you’re not limited to anything.
Your question implies an obligation to pick a scale and then use only chords of that scale in your progressions. Thinking that way, you might look at it as if scales are senior to chords. And for all modal scales, there is only one dimished chord and no augmented chord.
On the other hand, If you like to progress from one diminished chord to another, do so and then realize that you have modulating from one scale to another. Now you’re putting chords senior to scales, which is perfectly valid and workable (and probably more typical and more in line with the way you naturally think of music).
Along that same line, it’s interesting to take a chord and figure out all the different scales that you can play with it.
Note also that there is a scale beyond the modal ones that contains an augmented chord and two diminished chords.
Modal chord: c natural minor (aolian) c d eb f g ab bb chords by degree:; min, dim, maj, min, min, maj, maj
c natural minor altered c d e f g ab bb chords by degree: maj, dim, dim, min, min, aug, maj
If this got a bit too wonky for you, just takeaway that you can create chord progressions in any way that sound good to you, and figure out as needed what scale to associate with the various chords.
Appreciate the help, Dan!