It doesnt matter if the card is AMD or Nvidia.Used Nvidia on KT 333 2002-2009 no issues.
Had an 8800GT in a K2A9 Platinum with 790FX no problems.
The problem is that Nvidia cards are made to die fast ,in 2 years or so you have to buy a new one without the ability to sell the old one.
Thats why i have personally switched
If the card manufacturer is a serious one you will have no issues at hardwarelevel.
Conflicts between the 5770 and the Nvidia card can arrive at driver level when they are used in same time.
But you have to test yourself.