Everyone can get some Samnites in proper provinces to train, with the appropriate government and such; no region should be a total loss unit wise, though you will find that Celtic factions fare better in recruitment by conquering Celtic regions in Europe, which are plentiful, and will be able to get a fair bit of other, neighboring units (including an alright amount of Greeks, when done, with the proper governments, meaning conquering Greece won't be a total bust).