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I am using a hot wire anemometer.  It is just a simple narrow cylindrical probe with an slotted opening in the tip to expose the heated element to the airstream.  I asked the manufacturer how to use it to measure vacuum airflow and their recommendation was to hold the probe right at the opening.  No shroud or cone necessary since there is no rotating vane.  There is a white dot on the tip to tell you which way to orient the probe ( dot facing into the moving air ) but I have tried it both ways and it doesn't seem to make a difference.  You are just trying to get a raw airspeed measurement at the hose end.  From there you multiply the airspeed by the area of the opening and then multiply that product by 0.8.  Pretty straightforward.