Pool/Billiards/last pocket rules in pool
can you hit the eight ball in off your opponent's ball to win the game?
If you are playing with people who look to authoritative rules that are followed by all serious players, then yes, you win and it is entirely irrelevant if it kissed in off the opponent's ball, nor does that kiss does not need to be called. The proper rule is that you only need to indicate** the ball and the pocket—absolutely nothing about how the shot will unfold. This is true throughout the game as well as when you are on the eight ball.
If you make the intended ball in the intended pocket and commit no other foul (e.g., contacting you opponent's ball first with the cue ball or jumping a ball of the table, etc.) the shot is legal. You would win if it's the eight ball, or go again if it was a ball of you group during regular play. You can, for example, call the eight ball in the left corner (nothing else), then bank or kick it of three rails, have it brush four balls and if pocketed in the intended pocket, you win.
Now, these are the authoritative (and much better, more logical) rules, but you have to understand that a huge portion of the pool playing world play in casual venues, and do not know this rule and many others that make the game sane. In bars what you find is chaos; every player understanding some anecdotal set of rules they learned somewhere
, when such uncodified rules often vary between bars on the same street. One rule seen fairly often is that you must call every aspect of a shot—a rule that has surface appearance of requiring rigor, when it actually strongly favors unskilled play. Last pocket is an eight ball variant, and so even more than regular eight ball, may have some set of house rules in effect, such as that the eight ball must go in "clean". The house rules may be crappy but you can't persuasively argue anyone is definitely right or wrong unless everyone has decided what rules are to be followed beforehand.
I invite you to read the BCAPL (Official Rules of the Billiard Congress of America Pool League), the best most logical and nuanced ruleset there is: http://www.playbca.com/downloads/rulebook/completerulebook.aspx
Best of luck,
**For in-obvious shots—you need not indicate anything for obvious shots. The following are defined as "not obvious" shots: "bank shots, kick shots, combination shots, shots that include caroms, kisses or cushion contacts that are not incidental." So in your case, since it was a kiss shot, it would need to be called, but again, just the ball and the pocket.