ArcFM Server provides web services with a REST API so you develop against it with any client technology.
Great question. We currently only published API and samples in Silverlight however ArcFM/ArcGIS Server itself provides REST endpoints. These endpoints can be interacted with via HTTP calls. There is not reason you cannot interact with these endpoints using ajax just as you can with ArcGIS Server.
For an example: navigate to the rest sample service rest endpoint:
Here you can see the ArcFM extensions (/exts/) endpoints which was added to the server via the ArcFM SOE. At the bottom you will see several traces which can be performed. Click the link to test the traces and see the appropriate fields.