Yes, but you only need substitutions in a delimiter field to accomplish this. The below example would display the video field if it has a value otherwise will display an image field.
Code:
[cb:if cb_video=""][cb:userfield field="cb_image" /][/cb:if]
[cb:if cb_video!=""][cb:userfield field="cb_video" /][/cb:if]
Please see the below for further substitution usage information.
www.joomlapolis.com/support/tutorials/107-use-cases/18353-using-substitutions-throughout-cb
Note you can hide the video field if it doesn't have a value on profile view using CB Conditional you just won't be able to replace it with your image field using CB Conditional.