See Google Nest Device Access Console now available and Nest - Bindings | openHAB (follow the SDM instructions).
Both Arlo and Nest go through the cloud anyway. There is no local control or access for either of these systems. Arlo is completely closed as far as I’m aware.
A cheap Amazon Echo and the Amazon Control Binding could be another approach if you don’t want a SmartThings hub. It’s basically the same overall approach.
Not SmartThings but Amazon Echo. Amazon sent me a free Echo Show because they are ending their separate Amazon Dash service which let my printer order toner automatically. That feature has moved to Alexa and needs an Echo. Once I got it I added my thremostat and outdoor lighting, neither of which have OH support. I can now access them at a basic level using the Amazon Control Binding. It works OK. I’d prefer to have more controls on the thermostat though.
No because you can’t access Arlo nor Nest locally anyway. It’s all cloud access or nothing for both of those.