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NTSC TV uses the equivalent of 341.25 pixels per line
How do you figure that? NTSC doesn't use pixels horizontally at all. Or what do you mean by "equivalent"?
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Is that the same for NES video output?
No. As said previously, the NES doesn't use an interlaced display, and it also uses a different line rate than real NTSC.
The dot crawl pattern is largely a function of the relationship between the line frequency and the color subcarrier frequency.
Real NTSC uses a line rate that is defined as 4.5 MHz (the video bandwidth size) divided by 286, and defines the color subcarrier frequency (Fsc, 3.579545 MHz) as 455/2 the line frequency. In other words, in real NTSC, the line rate is Fsc * 2/455 = 15734.26573 Hz. The odd multiple 455/2 was chosen by the FCC deliberately so the color subcarrier's dot pattern would alternate and thus cancel itself out over time on monochrome TV sets. The "2/" part tells you that it's a two-stage pattern, meaning that artifacts cancel each other out after two fields (discounting interlace).
The NES uses a line rate that is Fsc*(6/4)/341 = Fsc * 3/682 = 15745.80112 Hz on even fields. The "3/" part tells you that's a three-stage pattern, meaning that artifacts cancel each other out after three fields. Which is what you get if the background had been off, like in Battletoads. It also tells you that the pattern repeats itself after three scanlines, which is always the case.
Since on odd frames, one scanline is shorter by one PPU cycle, the middle of the three pattern stages gets "skipped", thus you get only two stages of the three-stage pattern over time, so that the artifacts never cancel each other out completely over time.
Hope I got everything right.