This is NOT a scenario for playing; it's just for exploring the range of monsters and getting their numbers.
I procrastinated sleep a bit, wrote a couple of scripts, played around with some parameters, and came up with a combination map + mod for exploring all the monsters (numbers 1-1712 appear to be valid).
The map file is a 36-province map. It's divided into two zones of 18 provinces, one for Arcosephale and one for Ermor, since there have to be at least two players and I was feeling too lazy to do a version that's a disconnected map to avoid dominion-kill effects.
Each player's provinces are named 1-100, 101-200, ..., to 1700-1800. Monster #x is a commander in the appropriate province and has the number as the name...
...with certain exceptions. Namely, certain monsters automatically unsummon themselves. Hence, the provinces "1-100" each contain a new magic site, #900. This is intended to let you see these self-unsummoning monsters via the recruiting screen. However, only the first 5 #homecom commands take effect; the others are ignored. So if there's a commander you want to see, cut-and-paste the existing numbers (all the self-unsummoners I found are listed, sorted by type, with names) ahead of all the rest, restart Dominions (the mod is re-read at that time), and reload the saved game. Or, if you don't want to use the mod, just comment out the '#knownfeature' lines (both of them) in the scenario file.
Might be helpful if you want to see what you're missing out on by not summoning Doom Horrors.