I agree that Roth encouraged the Rosato Brothers to act up, leading to Clemenza's heart attack. This could have been by design. Clemenza was old, and hardly the picture of health, so the added stress certainly didn't help him.

More likely, the heart attack was merely a side benefit of what was really a Roth offensive in his war against Michael.

I believe Roth's tactics here mirror Barzini's in Sicily - covertly causing apparently minor trouble on the outskirts as part of a larger campaign against the Don.