On your first question :
As it is not recommended to mix data in such way I may suggest the following approach :
1. Using the HeaderCellTemplate property you may place the measurement unit cells within the header cells ( e.g. under the header cell). Inside the template you may place an user control of yours that displays the unit and shows a combo on edit.
Another alternative would be to use secondary headers and place this above the regular headers ( if applicable to your case.
In short - Yes it would be possible.
I will be glad to assist you in the implementation of this one.
On your second question :
Are you trying to implement some kind of context menu ? Let me know the details and I am sure we can think of some descent solution.
the Telerik team