Yes, the pitches on guitar are different from the (C) ukulele, but the intervals between the top strings of the guitar are exactly the same as on an ukulele in linear fleas tuning.
As for the markers, there's a fair bit of variation. Most standard are markers at least at the 5th, 7th and 12th frets; the 12th fret is sometimes marked with double dots or a more distinctive marker, and the 7th may be treated this way as well. Guitars tend to have a marker at the 9th fret whereas on ukuleles (now) a marker at the 10th fret is more common. Some guitars and ukes will also have a marker at the 15th fret and, less commonly, at the 3rd fret. Guitars may also mark the 17th and 19th frets. This pattern is also used for a number of other fretted instruments: my banjo has markers at the 3rd, 5th 7th, 10th, 13th, 15th, 17th and 19th frets. Note that banjo tunings typically have little relation to guitar tunings; it's not the tuning pattern that dictates the marker placement as much as the intervals above the open string pitch: the 5th fret marks an interval of a perfect fourth, the 7th marker corresponds to a perfect 5th, the 12th marker corresponds to the octave—the note names above the 12th marker exactly duplicate those on the lower fretboard. The other markers are more arbitrary, providing supplemental reference points between these main positions—unnecessarily, in my opinion; and in fact, I find that the increased visual clutter and uniformity confuses me rather than helps me to navigate.
My ideal marker set for an ukulele would be 5th, 7th, 12th (doubled), 17th, with 10th optional (I'd omit it on a custom), with side markers or left-edge markers mandatory. I've ruled out buying some very good uke brands because they omit the side markers, making all but pros lean over the fretboard or tilt their ukes out of best playing position. Egregious.
I can't help you with the history.