Well, I base this on a DVD from someone in Europe which will not play here in the US even though it is NTSC. And, I am not the only one with that problem. So, I hope to work out this "exchange" problem beforehand.
PE
That sounds like region locking.
U.S. is region 1. If you can still alter the discs you should ask them to make your DVD region free or region 0 or region ALL (either one), that will maximise compatability, as well as lack of bad/corrupt sector style copy protection, though your discs are not pressed as you said they're DVD-R's right? So I doubt they'd have that.
Many modern hollywood movie DVDs will not play on computers properly, and some TV DVD players, even with intermediate software like AnyDVD (until a new update comes out.. usually a bit late) due to such severe copy protection methods, such as corrupt sectors, and bad IFOs that violate standards. Symptoms include locking up, freezing and skipping... each time in a different section of the movie if you play it again.. I pay for not-in-cinema movies, yet I can't watch them, so I stopped and just download them now for a reliable quality experience.
In any case, its not hard to get around.
Random brand cheap DVD players are better than brand name, they have better compatabilitie, read more codecs for non-stand stuff simply read formats regardless what its on (DVD on a CD - 20 minute DVD eg etc), and aren't region locked.
Though you can get codes to unlock region locked DVD players here by ringing tech support (or looking online) as region locking is technically illegal in Australia (artificially limiting market choice).
NTSC vs PAL isn't a problem, one is 720x480 29.97 fps, the other is 720x576 25 fps (PAL), resolution is the same regardless of image aspect ratio. PAL vs NTSC was only a problem for old CRTs synced to the mains power supply (U.S. 60 Hz, Pal countries 50 Hz). Even old modern CRTs have both modes. And then many DVD players can output to either format anyway, so it's not really much of a problem.
You can also have a data section on DVD discs that accompany video, if you want to put a video file on there, or you could host one online via vimeo or something for customers, though that would likely get leaked publicly quickly.