Yes, you should be able to use any valid PCRE.
Splunk's documentation can explain this much better than I:
http://docs.splunk.com/Documentation/Splunk/6.3.0/Knowledge/AboutSplunkregularexpressions
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You could do something like this:
...
<panel>
<table>
...
<drilldown>
<link>your_employee_detail_report?Emp_ID=$row.Emp_ID$</link>
</drilldown>
</table>
</panel>
...
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