How strongly is a product marketing certificate from the Pragmatic Institute viewed in hiring for a product marketing manager?

I’ve never heard of this particular certification. That doesn’t say much - I’m not your typical PMM. But in general I’d say experience, work samples, business case interviews, and references matter more to me than any outside certifications. To my knowledge we don't really look at that much.

If you have it, display it. It never hurts to try to differentiate yourself from the competition in a highly competitive field, especially if you don't have relevant bachelor's degree in business/marketing or an MBA. Some employers and hiring managers will care, others won't. But nobody will see it in a negative light.