Pretty much every winch uses the same bolt pattern so there is no reason to make the mount adjustable allowing the possibility of the winch moving under load or flex in the deck which is very bad. As long as the bumper manufacturer makes sure a Warn Zeon fits (they are one of the portliest winches out there) every other winch out there will be fine.
How does the concept of bolt torque and clamping force apply to the winch attachment to the deck?