Hi Anthony,
it is certainly possible to use other tools that achieve the same outcomes as SLP.
It gathers information from the Server logs either by making repeated calls to the REST endpoints or by directly reading the log files themselves.
The magic is in how the raw information is turned into useful statistics.
I would say it is not reasonable to ask for the source code for how this is done.
You would need to gather log start transaction and end transaction records grouped by transaction-id and do the maths for the duration.
Then collate a table/dictionary of all transactions and retrieve the various statistics
- time of day, duration, success/error codes, etc
then use this dictionary to create useful reports.
or, you could write code that calls SLP.exe to gather the stats and report with your dashboard tool - that's how ArcGIS Monitor does it
Good luck in your endeavour