To make sure that I understand
1) You are using the TBC Dimension command to dimension things in the project
2) You are adding those Dimensions to the data selected for the Design for an SCS900 Project
3) In SCS900 you get the Lines not the Dimension Arrows or Text
4) You are using SCS900 not Siteworks?
You can Explode the Dimension Objects in TBC v5 and export the components to the DXF file in a Design and they will look like this in SIteworks - my guess is they will look the same in SCS900 as they are just Lines and text after exploding - this was a VCL file with Exploded Dimensions

This was a DXF File with Exploded Dimensions

There does appear to be some issue in the DXF read / VCL Read by SCS900 / Siteworks that gets the text justification off centered (I Think the software just places a standard Text on the drawing (it doesn't appear to understand Fonts, Sizing, justification etc. from either DXF or VCL)
I will send the product team this feedback but this at least gives you a path to get the Dimensions out to the field. I think the DXF will work the same in SCS900 if you are still using SCS900 not Siteworks. DXF appears to do better with the Text than Siteworks
Alan