Depends on the supplies, but the diodes help a lot. A problem with them is the negative temperature coefficient of Vf. Whichever diode starts out conducting more current heats up more, it's Vf decreases, and it becomes even harder for the other supply's diode to conduct. Some of this effect is offset by the way Vf increases with current. Still, you need to be able to adjust the two supply outputs fairly precisely to get anything close to 50/50 sharing. If the load and ambient temperature are constant, then maybe. Otherwise, one supply at 100% rated current and the other at only 80% might be all you can sustain.
ak