Not a Linux expert nor expert on VSEL but the agent is essentially the same across all platforms.
It has 3 main components: scheduler, updater and a management component. In a standalone install (no ePO) only the updater and scheduler are active once under ePO management, the management component gets activated as well (for policy enforcement, epo communication). Therefore the agent is a critical component also for a standalone install.
There is no problem in installing the agent twice, all the second install will do is "enable" the management component, drop another sitelist and several other bits and bops that are essential for ePO communication, thats it.
Thanks for confirming, I had a feeling that would be the answer. I obvisouly forgot to mention the updater component in my post which is kinda important, but thankyou for your concise and complete answer!