The caps on the "MX-Board 2.0" (G80-3800) and "MX-Board 3.0" (G80-3850) are not perfectly 0 degrees, but a little less than the home row of other cylindrical profiles. It is only that reduction in angle that makes them the lowest-profile Cherry MX-compatible keycaps: because the front edge is lower. The back edge is as low as the back edge of "Cherry profile".
Note that if you use lower-profile keycaps on such a highly contoured keyboard such as the Dactyl, the keys' tops will be farther apart on the vertical than with high-profile SA keycaps.
I would go with R2 DCS. I think that a little bit of forward angle is not that bad, actually. I think you'd want to be able to feel a little bit of front edge.
Otherwise, I think that top-row "Cherry profile" could be closer to 0° and they are slightly higher, but they could be more difficult to source. (I myself got a bunch blank ones, once... but that was because a member made a special order for them, got a high Minimum Order Quantity and had to sell the spares to be able to make the order)