Is it the case that we can switch from our on-prem license server to a managed license server that Dassault hosts for Solidworks? 

From 

"Managed DSLS is also known as Managed Licensing Service.

With Managed DSLS, an on premise customer no longer needs a physical machine to install DS License Server (DSLS). The license server is managed by Dassault Systèmes and located in Dassault Systèmes Cloud datacenter.