Not as much as running with a football equipment on... and I'm seeing plenty of players with great sprinting technique. The keys are:
Doing a lot more running/sprinting work without the vest that with one (at least a 3:1 ratio)
Not going too heavy (for sprints there should be no more than a 10% drop in speed)
Not doing only weighted running in a session. Everytime you do weighted running also include regular running. Ideally in a complex (easier to do with sprints than endurance work) and always ending with un-weighted running
As far as using one for conditioning work... well most people already use a sloppy running technique during conditioning work so it likely wont make a big difference.