Well, yes & no really.
The thing for Dolby Digital (AC3) on a DVD that is to be released to the public is that it should never be encoded on anything except a properly approved encoder - it is not free technology, and all the free ones are either reverse engineered or hacks (or in the case of Sony Vegas, a loss leader to get you into their system)
The Dolby Licensing is dependant on the tool you use more than anything else - which makes sense.
I fully agree we should have this built in to Nuendo - as we know it did exist & then it was withdrawn along with the DTS encoder, and there are very few plugin versions available - the only ones I know of are for Pro-Bloody-Tools only so the cheapest workaround is to grab a Minnetonka Audio standalone one from http://www.minnetonkaaudio.com/index.php?option=com_content&view=article&id=51&Itemid=80&lang=en&phpMyAdmin=2f8ebc5437f1c9t59fb7cb7r58337 and it is far from cheap at almost $600.
If you have Adobe’s Premiere Pro there is a plugin encoder for this at half that price (same place - SurCode for Premiere Pro) and Dolby themselves do one but it is for Mac OS only and part of a VERY expensive toolkit (which is frankly insane IMO)
If you are stuck & need something doing, drop me a PM and I will happily help out a fellow Nuendee from a tight spot.