For those that google this, I tried doing just this.
Using Windows 10 and 376.33 drivers
With 4k UHD connected by displayport which is the only option that gives 60hz, 2 displays connected by DVI, and a fourth by HDMI to DVI passive, all displays did work but with major bugs. Fullscreening anything on 4k monitor, especially 4k content frequently causes slowdowns, glitches, display driver failures, and crashes.
4k UHD via DP + 2 1080p displays connected via DVI seems to work much more smoothly so far. Experiencing none of the issues I complained about including slowdowns.