They can deploy all the troops they want. The question is do they have the will to do what is necessary to keep them out? This might include shooting people. Or will they just stand there and merely help usher in the influx?
My hunch is the latter.
They were okay when they were just an in-transit way station for the influx outbound to Germany. Now that Germany has said “screw it” and tightened up, they realize that the “buck stops there [Austria].”