If you meter a gray card with any reflected light meter, the results should be quite similar to what you get with an incident light reading. While the ISO calibration equation allows for a manufacturer-chosen variable value, which can lead to differences in readings between different brands of meters, the results should be within 1EV of each other at the most.

If I compare my Minolta Vf incident meter to my Minolta Spotmeter F pointed at 18% gray card compared to my Canon dSLR pointed at 18% gray card, all three readings match each other. But I consider that more 'luck' than 'expectation'.