It is probable. I can't find perfect specifications, but the dimensions of the Pro 3 and Pro 4 are very similar. Lining up the machines visually, as shown in the image linked below, indicates that the dock port is in the same place and is the same size. That's by no means proof but it's not ruled out. The USB and DisplayPort certainly change by comparison.

I have ~20 Surface Pro 3's in production so I am very interested in this answer.

Surface Pro 4: 11.5" x 7.93" x 0.33"

Surface Pro 3: 11.5" x 7.93" x 0.36"

http://i.imgur.com/aUCyzLi.gif

Again, this is a sloppy image comparison, not a guarantee.