Standard video DVDs use the UDF (Universal Disk Format) file system. UDF DVDs will play in standard DVD players, and OSX will start the DVD Player application when a DVD in UDF format is inserted (unless settings have been changed in the "CDs & DVDs" system preference).
Finder and Disk Utility cannot create UDF DVDs, although Disk Utility can copy an existing UDF DVD or disk image file. iDVD (part of iLife) can create UDF DVDs, but only when encoding video files, not from VIDEO_TS folders.
If you use Finder to create a DVD from a VIDEO_TS folder, the DVD will appear OK in finder, but will not play in most DVD players, and OSX will not start the DVD Player application. It should play if you drag the VIDEO_TS folder to the DVD Player dock icon.
You can create UDF DVDs with Burn (free).
<http://burn-osx.sourceforge.net/Pages/English/home.html>
Select the "Video" tab and set the format to "DVD-Video". Drag the VIDEO_TS folder to Burn's widow and use the "Burn" button, or "Save Image" from the "File" menu.
Be sure to use good quality DVDs, such as Verbatim DVD-R or DVD+R DL.
You could have the DVDs sent to you as a UDF disk image files, instead of a VIDEO_TS folders. Those can be burned to DVDs via Disk Utility, and the DVDs will play on standard DVD players. The VIDEO_TS folder will be inside the disk image file, so is still available if needed.