Not sure I see the value in Peplink doing so - would also be interested to hear more about the demand.
Had someone else ask about DMVPN recently: Dmvpn cisco Vs Peplink speed fusion - #2 by MartinLangmaid and my views on it are still the same - you can do more with SpeedFusion / SD-WAN than with DMVPN so SF wins in my opinion.
If you’re looking to integrate new SpeedFusion infrastructure with an existing DMVPN solution then I would recommend keeping them separate and using BGP as the bridging protocol (or just static routing with a sensible subnet topology) at the core/hub location.