If user would like to use regular expression for alarm filter on dashboard portlet, operator has to be "matches".
Here is an example procedure.
1. Create a widget on dashboard portlet.
2. Select the widget, then open [Widget Properties].
3. Browse [Data Source] and set [Type] to "Alarm".
4. Add data source, then alarm filter.
5. Set operator to "matches" and input regular expression to field.