YES. For example, the WS2188 chipset is almost identical, except for a couple details:
Both are 800kHz.
Both have data ‘0’ as 0.25uS high followed by 1.0uS low.
UCS2903 data ‘1’ is 1.0uS high followed by 0.25uS low.
WS2811 data ‘1’ is 0.6uS high followed by 0.65uS low (in theory too short a high).A
All though this does not meet the UCS2903 spec of 1.0uS to 0.25uS it is close enough to run these pixels.
UCS2903 reset is greater than 24uS.
WS2811 reset is greater than 50uS (old type) and greater than 280uS (new type).
This should be fine as both WS2811 reset times are greater than the UCS2903.
The reason not to mix WS2811’s and UCS2903’s on the same data line is that the data timing that works with both types of pixel is regenerated by a “UCS903 or WS2811” pixel of which ever type the timing becomes specific to that pixel type and unlikely to be recognized by the other.
That said WS2811’s may run on UCS2903’s data but not the other way round.