Hello Denis,
flags from "Business Partner Type" area come from BBPM_BUT_FRG0011 table.
Indeed, this table is used for search Bidders query. Nevertheless, it is not used to search for Suppliers (only BBPM_BUT_FRG0061 is used): have a look at EXECUTE_SEARCH_SUP method from /SAPSRM/CL_PDO_SO_SEARCH_BUPA class.
So, to cover your request, use Enhancement Spot /SAPSRM/BD_CLL_POWL_FEEDER to implement /SAPSRM/BD_POWL_CHNG_SEL_RSLT BAdI definition in order to filter out partners.
Regards.
Laurent.