Excellent question.  I do not have any historical evidence of widespread tank vs. tank ramming, and I don’t really expect that it went on.  I included the rule more for sake of gameplay with non-armored vehicles (jeeps, halftracks, etc.) The rule represents a sort of last ditch option available to a player with nothing left but jeeps who is trying to face down a tank.  I’ve people ask to be able to ram on a number of occasions, so I decided to come up with a rule for it.  The attack itself is pretty anemic (need 6’s to hit) so I can’t think of why a tank would ever choose to ram another vehicle instead of using it’s short/medium range armor attack roll instead.  Now a jeep, on the other hand, really wouldn’t have any other attack against a light tank.  With the ram you might be able to damage a tank, but you are certainly going to destroy your jeep trying.  Let me know if you end up using the rule and if it works for you or not.