I've yet to see the nvidia installer successfully deal with nouveau.
I've been getting a lot of system wide crashes with slackware. First I thought it was the flash plugin, but it crashes without it. Then I thought it might be the 64bit version of slackware, so I installed the 32bit version but the crashes carried on. I'm talking about system wide crashes where either the entire box locks up solid or everything except the mouse locks up solid. So I switched to SalixOS Mate version, presuming this to be some sort of KDE issue - no more crashes.
SalixOS Mate also deals with nouveau appropriately (as long as one adds it to the excludes list in gslapt, which otherwise wants to remove the blacklist file and reinstall the nouveau driver).
I miss KDE, but I'm hazarding a guess that Slackware 14 isn't all that far away, so will return to pure slackware when that's released.