Even if the random password seems not listening to the custom password policy, but the user will be prompted to change the password after the policy is applied, as customer password is taken into effect, then the user has to change the password in order to meet the policy requirement.
other known issues: SPR # GFAL98TM4S(Random password reset in vault server error password does not meet the requirement)
Note: to understand this SPR please look at Dev's comments:
IBM Domino Admin doc: "Custom password policy settings will not: support random password generation...."
However, support for the minimum password quality/length may be added.