Shutterstock has never transferred metadata for me when uploading clips, images are not an issue though.
Also, keep in mind that Bridge replaces all commas , with semicolons ;
Now as far as I can remember Shutterstock had no issues with this but I reckon there has been a change recently and now it removes all keywords, probably because it sees it as one big keyword.
I use a copy/paste on a text file and then auto replace the semicolons back to commas.