Having multiple pointers in one gauge is not possible at the moment. If you declare several sets of settings only the last will take effect, as with any other ASP server control.
The idea that a gauge should have multiple pointers is already logged for research and implementation and you can cast your vote, leave a comment and follow its progress here: http://www.telerik.com/support/pits.aspx#/details/Issue=13368
For the time being you can consider placing two identical gauges on top of each other with CSS with the only difference between them being the value (and/or color) of the pointer.
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