Thanks. DTM holds the AA tracker object in an enclosure which prevents it from conflicting with other code at window scope.
When you use the setting, "Managed by DTM", by default, you cannot reference the 's' object at window scope. Typing window.s in the console WOULD NOT return the AA tracker object. Typing window.s.t() would not cause a beacon to be sent.
Within DTM, in the context of the AA Tool (like in Custom Page Code of the Tool Settings, or in the AA custom code section of a DTM rule) you will reference the tracker as 's', but this will map to the local scope and will not map to the window scoped 's'.
In short, you SHOULD not have any conflicts to worry about.
If the other code on the page that uses 's' is another Adobe Analytics implementation, then there are a few gotchas because there are some functions (even in the 'Managed by DTM' scenario) that can cause some issues. I'm thinking specifically about the function, s_gi which returns an instance of the tracker. If your other code using 's' is not Adobe Analytics, you should be just fine.
If you need to reference the AA tracker from outside of DTM and you need a name for it other than 's', you can add a line of code to your AA Tool settings in "custom page code" like so: window.s_xyz = s
I think that covers it. Please let me know if this answers your question.
-Stew