Hi,
It is possible to create the hierarchy from the issue picker fields in eazyBI with specific advanced settings. The limitation is that eazyBI cannot build a hierarchy if the child can have several parents. In other words, the issue picker field must be of single-issue picker type at the child issue, which seems not to be your case.
The approach with the multiple user picker field is to create a multiple value dimension from this field with advanced settings like this:
[jira.customfield_NNNNN]
data_type="string"
dimension=true
multiple_values= true
separate_table=true
NNNNN is the ID of the issue picker field. Once you import this field as a dimension, you can combine the new dimension with Issues and see the report like this:
Kindly,
Janis, eazyBI support