The "redirect printers" feature is not currently supported for HTML5 bookmarks. Currently only ActiveX and Java bookmarks support this feature.
At the moment there is an enhancement request opened with our engineering department to add this feature on HTML5 bookmarks (DTS 155574). According to our engineering department, this is planned to be released with the 8.6 firmware version which will be web posted in the beginning of 2017. Please note that this date may change. If you need more information, please contact the SonicWall Technical Support.