I have a Google Analytics property with lots of historical data.
I want to track certain server-side events using the Measurement Protocol, PHP, and curl.
However, I have only been able to get this to work using a new, blank property.
The property that I need this to work on has been upgraded to Universal Analytics with about a week.
Can I use Google Analytics Measurement Protocol with an existing property?
According to Google's documentation regarding the measurement protocol, "The Measurement Protocol is part of Universal Analytics, which is currently available in public beta. Data from the measurement protocol will only be processed in Universal Analytics enabled properties."
So as long as your property has been updated to Universal Analytics, yes, you can use it with an existing property.