i dont think that will be posible, though you could edit the inital array to use both sources, so instead of using:
var tags = [ <?php do { ?>"<?php echo $row_rsCategories['category']; ?>",<?php } while ($row_rsCategories = mysql_fetch_assoc($rsCategories)); ?> ];
to populate the array, use:
var tags = [ <?php do { ?>"<?php echo $row_rsCategories['category']; ?>",<?php } while ($row_rsCategories = mysql_fetch_assoc($rsCategories)); ?><?php do { ?>"<?php echo $row_rsKeywords['keyword']; ?>",<?php } while ($row_rsKeywords = mysql_fetch_assoc($rsKeywords)); ?>];