I am alittle confused as to what you are saying, Are you referring to the Nuance voice commands as separate app. I can get that to work, but it is sluggish and less accurate than the google search version. There is a google video demonstrating voice actions from inside of voice search. I think this is supposed to be part of the stock rom, no need to download a separate app. That said there is an upgrade on the market for google search that becomes available once on 2.2. With or without this, the prolem still exists.
My understanding is that in Froyo, the google search app shound first interperate the words that are being spoken. Then based on what phrase it desides has been said either performs a google search on the phrase, or if the phrase contained the right opening keyword, such as "call" or "email" or "map" or "directions", it issues a 'voice action' command to the associated app. Eclair did this with some apps such as calling reasonably well right from the stock google voice search. In Froyo, the abilty of voice search to understand what is being said I would say is improved. However, it drops the ball when it comes to passing the intended command to the app. Oddly, It will call any resturant or bussiness not in my contacts with total reliability. Something is wrong possibly when the voice search recognises the keyword "call", executes the voice action assoicated with "call" (the dailer) and then finally gets confused when it somehow fails to find the contact requested, even though it is in the google contacts.