Ok, for some update.
The sriov_drivers_autoprobe thing works, and is what you should use. My error was that the 0> confused the shell to think it was about redirecting stderr. Doh! That is, put a space between, like 0 >, then disabling the autoprobing works.
For kernels that have the sriov_drivers_autoprobe file in sysfs, there should be no need to touch the probe_vf parameter, either via /sys/module/mlx5_core/parameters/probe_vf or by adding the probe_vf=0 option when loading the mlx5_core module.