I150 combat gear does not turn into Tier 5 Materia, as far as I know. That would imply that i150 crafting/gathering gear will not turn into Tier 5 Materia, either.

I have not seen any gear between i150 and i170, for crafting/gathering, have you? The current lowest known ilevel to convert to Tier 5 Materia is i160. So ... yes, expect to have to convert the i170 RCS+RGS blocked stuff for Tier 5 Materia.