A designed rectifier will take some care about distributing
forward current for high-current survivability, and maybe
even try to make reverse breakdown (to some current level)
well behaved.
A MOSFET has diodes but it's evident that some device
designers have not expected the parasitic diodes to conduct
significant current, the Vf of the diode is not of interest
(though these may indeed matter to a power supply designer
and BOM cost would like the diode to be useful enough to
dispense with an external backstop). There are "avalanche rated"
MOSFETs which survive repetitive breakdown (up to some Joules
per stroke) and there are ones which are not.
If you're "off the map" then it's time to do your own abuse
testing (but realize than an unspecified attribute stands to
wander, drift, be changed over time, and for production you
would be best off to have a part that specifies what you
care about.