[Ygorl]

Psientist, you don't want to use the "open" command. Just type /Applications/Games/Dominions 3/Dominions3.app/Contents/MacOS/Dominions3 -h
and you'll get your list.
Note that if you want to run the game this way, say if you like using a nonstandard resolution, you have to run it from a slightly different location (search the forum for other posts by me and others to see how) - but if you just want to run the command-line version (to get help, verify turns, host a turn, etc.) this works fine.
I don't know if open has support for command-line switches to the program you're opening (open is really designed for opening files, not running applications) but even if it doesn you'd probably have to put it in quotes. Anyway, you don't want or need it in this case. Hope this gets you what you need.