1) You may put your desired custom date/time format string for the customDateFormatString parameter in Cells.importResultSet() overloaded method. See the sample line of code for your reference:
e.g
Sample code:
worksheet.getCells().importResultSet(rs, 0, 0, true, "d-mmm-yy", true);
2) It is better once you have imported data to Excel worksheet using Cells.importResultSet() method, you may apply your desired number formatting to the cells in the range/column accordingly, see the document for your reference:
http://www.aspose.com/docs/display/cellsjava/Setting+Display+Formats+of+Numbers+and+Dates
In your case, you should set the custom number format string as "$#,##0" for your requirements.