I have been hearing conflicting things about whether or not modern PAL players and sets can also play NTSC DVDs as well. Is this true?

Yes, but not visa versa. Pal can play NTSC, NTSC cannot play Pal. Well, 95% of Pal players anyways:

http://www.dvddemystified.com/dvdfaq.html#1.19

Kevin

Well, I would not say yes. Here's how it boils down currently in western
europe (at least here in Holland):

1. almost all DVD players have an option to convert NTSC to PAL on the fly

2. a lot of the medium and high end TV's can playback NTSC (especially the widescreen models).

So there is a pretty good chance someone in (western) europe can play back
an NTSC DVD. I'd say that chance is 75% (a "feeling").

However, if you want to sell a product on the PAL market you really can't
sell a NTSC version. Just convert (or have it converted) to PAL and sell that.

If it is for someone you know in a PAL country it should be fine to send
something as NTSC.