OK, let me make sure I understand. You want the S3 to act as a standalone phone- you give out the watch's number and people call or text directly to it. That will certainly work. In addition, you want to pair it with a smartphone to receive other notifications. That will also work. I don't know about NumberSync, but simple call forwarding can route incoming calls to the smartphone to the watch. If your peeps call your watch number it rings only the watch, if your customers call your work cell number it rings the watch and phone.
To the extent that you're OK with your "personal phone" S3, being essentially a dumb phone, while the smart aspect of the S3 is derived from your company smartphone, it will work. If you are allowed to put personal stuff (ie. email, FB, Twitter) on the company smartphone you'll have access to that from the S3. If not, then smartwatch dependent functionality of the S3 won't be accessible on the personal side.