Hi Björn
I have only played around with it briefly(prometheus + Grafana - NOT splunk), and you can export vServer stats directly from NetScaler, no need for ADM.
I use ADM/Console for WAF + BOT Monitoring + GW Insights. its a love / hate relationship, as there is many good things, but i tend to run into bug after bug, which complicates things. However, i keep support and engineering on there tippy toes 🙂