According to https://wiki.musicbrainz.org/Release_Editor_Seeding both primary and secondary types can be seeded using the "type" parameter. However nothing actually happens when secondary types are seeded, they just get ignored.

See attached example file. Seeding "album" works fine, seeding "compilation" (secondary type only) results in no selected types, "album" and "compilation" (one primary, one secondary) results in only "album" selected" and seeding "compilation" and "live" (two secondary types) results in no selected types.