If you believe Sutherland's (and I'm pretty sure most of us do), the taper is the same, 2 degrees per side for a total of 4 degrees. As [MENTION=170983]Ghrumpy[/MENTION] said (and according to Sutherland's), SR made a crank with 3deg, which given the context of Sutherland's comment means per side. Those are extremely rare, though I think I remember seeing one on ebay last year.

The difference between ISO and JIS is not angle, it's nominal width. I don't recall which is which. Since it is a taper the crank arm will always go on and seat properly, subject to two limitations.

If the spindle is wider the arm won't go on as far as it should. The chain line will be affected because the arm will be slightly too far outboard, but if the spindle is nominally too short the chain line may be fine. There won't be as much contact between arm and spindle as it was designed to have. If the rider is big and strong the inside of the aluminum arm may deform and the arm may even break. If the ride is lighter and spins rather than mashes, it may not be a problem at all.

If the spindle is narrower the arm will go on too far, with two possible consequences. The spindle may protrude past the hole in the arm so that the crank bolt tightens against the spindle instead of the arm. The arm may bump up against the flare at the inner end of the taper before the sides are seated.

Neither of these issues is guaranteed to come up. For example, if the taper is wider but just slightly longer than spec in the outward direction it could accommodate a smaller hole, since it is effectively a narrow taper with "too much" length at the wide end. It could accommodate a wider hole as long as the extra length isn't so much that it sticks out too far.

The point is, some combinations may work even when not ideal.