Hi,
ArcGIS Indoors (nor Indoo.rs) doesn't provide by itself an IPS, so you'll always need a separate IPS. ArcGIS Indoors is compatible with different IPS providers products and protocols, so you may use for example BLE Beacons with iBeacon protocol. Precice depends a lot of the BLE Network setup, calibration and facility.
ArcGIS Indoors is integrated with Indoor.rs, but if you need more customized behaviour for mobile side than ArcGIS Indoors application can offer you should use the SDK provided by Indoo.rs.
I assume Indoo.rs and ArcGIS will become more and more integrated in the future. Survey123 can be used with ArcGIS Indoors just fine (you need to specify the service address in ArcGIS Indoors configuration).
BR,
-Tom