Hi Scott
Here's a method that works for me.
Look at the Properties for the point feature class and click on the Elevation tab and set 'Features are' At an absolute height and either tick Geometry z-values (if your feature class is 3D already) or tick 'A field' and specify your elevation/depth field (this is shown in the clip below). Note that you need to have the feature class in the 3D Layers section of the scene contents or they won't show in 3D.
I hope this helps.
Stephen