CONNECT - Where is the Dimension Radial tool?

Your correct this has been removed, this and other superseded and removed features can be found in the Readme. ( Extract below )

C:\ProgramData\Bentley\Documentation\MicroStation\10.0.0\en\htm\ReadMe\GUID-C85CA707-5B2B-44E7-BA29-2AFFF35D4C4A.html

Radial Dimensions toolbox  

The Radial Dimensions toolbox has been removed along with the following tools within it:

•Dimension Radial

•Dimension Diameter

•Dimension Diameter Perpendicular

•Dimension Radius (Extended Leader)

•Dimension Radius/Diameter Note

•Dimension Arc Distance

Note: Place Center Mark is now accessible from the Dimensions toolbox.  

You can reference in a radial dimension from an older file. I tried it and it worked.

Open the Dimension Element tool. Once you click on the circle or arc it will switch to a radiusor diameter mode.