So while the risk you face may be the same, the damage that can be done is vastly greater. But I'm sure you're aware of that.
Assuming someone gains root level access to one of the boxes bastio is hosted on, then he could
1a. block all outgoing traffic from the server except for the service (to avoid alarms getting through) or 1b. replay the heartbeat sent by the server 2. retrieve the database 3. Sniff on all incoming traffic for the HttpOnly Cookies
The worst thing is you might not even know which customers' keys are compromised.
I'm sure you are thoughtful about security, but of course you are a great target because of the valuable loot (root access lot's of other servers)
A lot of your concerns are considerations for me too as I am thinking of launching a distributed SaaS. Just take it as input to your threat analysis :)