Are there any (visible) differences between R1 and R2 DVDs (or blu-rays, thereof)?
There is no visible difference, unless the DVD/BR publisher labels their discs as such.  Any region code (or even region-free data) can be burned or pressed on to any media.

Furthermore, region encoding (at least on DVDs, and I assume on BRs) has nothing (technically) to do with the video format.  Now, you're likely to find Region-1 DVDs in NTSC format, Region 1 is the U.S. and Canada, and the U.S. and Canada use NTSC, but there's no technical barrier to creating a R1 DVD in PAL format.

See the Wikipedia article on DVD Region codes, and specifically the section on NTSC vs. PAL.