Personally I would not listen to Philips support and try the non-DivX files out myself. You might be surprised.
If you have already converted the XviDs to DivX then yes; burning the files to DVD using the Nero ‘Data’ template will not result in them being re-encoded to DVD-Video (.ifo, .bup, .vob etc).
For the future, if you don’t know what are the encoding characteristics of a file, then you can download and use Gspot (version 2.70a from here). Drag and drop the file onto the Gspot window and it will tell you lots of useful info about the file.
Another useful program is MPEG4 Modifier (from here), which will allow you to alter the ‘User Data’ in the file. You might even try changing the ‘User data’ of the XviD encodings that you have, to the same as your DivX files that do play; and see whether they play then