As of October 2019, the answer is no. Polymath is not currently listed on Coinbase. However, this could change in the future as Coinbase has been known to list new assets on a regular basis. Polymath is a security token platform that is designed to compliant with securities regulations.
Security tokens are a new asset class that are slowly gaining traction in the crypto space. If Coinbase were to list Polymath, it would likely be one of the first major exchanges to do so. This would give Polymath a lot of exposure and could lead to more adoption of security tokens.