There are very few alfalfa producers who wait until their alfalfa has gone to seed to cut it. The only way you'd get volunteer RR alfalfa in a field would be to plant RR alfalfa and then let it go feral -- as one does in dryland alfalfa production in dry pastures here in the west.

Volunteer RR corn/beans/etc is a problem because you're allowing those plants to go to seed -- after all, you're harvesting the seed, not the plant. In alfalfa forage production, if I allow the plant to go to seed, I'm a pretty poor alfalfa producer. Most of my alfalfa is cut before the field achieves the bud stage. It is rare that I cut alfalfa in the bloom stage. It never, ever gets to the point where it can set seed.

Now, alfalfa seed producers, producing RR alfalfa, they might have a volunteer issue. But with alfalfa killed so easily and well with 2,4-D -- I really don't see it being a problem. One quart of 2,4-D/acre in a well-watered alfalfa stand and it will be toast.