I’ve done a bit of searching on trying to compile Nvu and KompoZer on an Intel Mac and it would appear to be very difficult without lots of patches that have already been integrated into the Mozilla source code. They are both based on some old Mozilla/Gecko code. Namely the 1.7 aviary branch, which did not support Intel Macs.
In the mean time I can use KompoZer (a bug fix release of Nvu) though Rosetta, which seems to work. Ideally they need to be based on newer Mozilla/Gecko code so that they can be compiled as a Universal Binary for Mac OS X, thus run natively on Intel Macs.
Update 2023: The above websites are no longer in use. There is still ongoing interest and it’s being hosted at https://kompozer-web.de/en/ now.