Thanks a lot for the detailed update.
If you are not interested in the Edit functionality of RadGrid at all, using template columns with ItemTemplate is the way to go. In case you want to use the Grid's editing functionality, though, the Client-Side bound RadGrid can only be edited using BatchEdit mode.
Or you can use any other means to send AJAX requests to the server for inserting/updating records and bind the response to RadGrid: https://demos.telerik.com/aspnet-ajax/grid/examples/data-editing/insert-update-delete-client/defaultcs.aspx
Basically, you can do anything in the ItemTemplate. For convenience, I am attaching a sample project demonstrating a way to use RadGrid bound on Client-Side with Template Columns, which contain Server Controls. You can see that it will render without any problem but BatchEditing is the only built-in option to edit the Grid bound on client.
If none of these options are applicable to the target by you scenario, you may also consider switching to Kendo Grid that was designed completely for the client-side:
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