Hi Yui,
We are still testing. I was able to add the initiator per smriti's instructions in the MSMP workflow, however we are integrating GRC with IdM so requests are being passed to GRC for an SoD check specifically. I do not know if the use case we are setting up would be beneficial to your question of whether or not the line item level would be processed for this initiator, but if we are able to test that I will let you know.
Your best solution may be to create the BRF+ custom initiator via DOC-45753 which should allow you to configure down at the line item level I believe. To run the simulations and testing that you are requesting, you'll need a access request number that has been submitted with the testing scenarios that you've mentioned (i.e. user request with no roles or role with inherent SoD violation). The simulation of your initiator should allow the rule result to show the routing per your decision table.
Hopefully this help,
Darnell