You very rarely see this happen at all. You will see motion, but generally speaking they won't move 3 yards and then back 3 yards. You also have to remember that the play clock is much longer in the NFL than the NCAA. In NCAA football you normally don't have time to motion. I watch hours and hours of football on Saturday, you see alot of motion but it is usually for reasons other than man or zone. In college they lineup and run the play. And there are plays you can motion the WR 3 yards and they will stop. There are plays where you can motion the WR and snap the ball while they are in motion.
And just because you motion you still won't necessarily know if they are man or zone. There are plenty of man/zone combo defenses out there. Don't you think defensive coordinators teach DB's and LB's to react differently to motion so that the offense can't get a read? Also, what about the 50 plays you watch every game and don't see motion? Motion is used for various reasons including to get movement to cause a defensive match-up problem. Also used to add a blocker.
The biggest thing is, on NCAA the series it is pretty lame to motion back and forth. If you have to motion back and forth to find out man or zone then you need to trade the game in. Call a play that has routes that will beat man and zone. Make your read and when you snap and throw the ball to the route that should be open.
Here is Bill Walsh's guide to motion.
By Bill Walsh
Quarterback Reads
Instructional notes from Stanford
A. STRONG SAFETY = PRIMARY KEY; SECONDARY KEYS = WEAK SAFETY, THEN WILL LBer:
1. STRONG SAFETY UP = SKY ZONE
2. STRONG SAFETY HEAD ON TIGHT END = MAN ( CHECK WEAK SIDE FOR BLITZ )
3. STRONGSAFETY & FREE SAFETY DEEP = DOUBLE ZONE
4. WILL LINEBACKER WALKED OFF = COMBO STRONG ( DOUBLE ON FLANKER )
5. WILL LINEBACKER UP & WS UP = BLITZ ( STRONG SAFETY HEAD ON TE )
6. SAM LINEBACKER WIDENS ON L.O.S. = BLITZ
B. MOTION:
1. BACKFIELD - NO MOVEMENT = ZONE
2. BACKFIELD - LINEBACKER MOVEMENT = MAN UNDER
3. BACKFIELD – DEFENSIVE BACK MOVEMENT = BLITZ
4. TIGHT END - NO MOVEMENT = ZONE
5. TIGHT END - SAM LINEBACKER MOVEMENT = MAN UNDER
6. TIGHT END – STRONG SAFETY MOVEMENT = BLITZ
7. FLANKER - CORNERBACK MOVEMENT = MAN
8. FLANKER - SLIDE MOVEMENT = ZONE