sneek does not require any files on a usb hdd. I'm pretty sure sneek+di still requires at least one game in usb:\games\ or usb:\wbfs\ for it to work properly. And it can take up to 10 minutes to boot a freshly made modmii nand, and if it takes longer than that, sometime it works after doing a hard power down and you start neek a second time and wait a little longer. Also, if you can't get a modmii emulated nand working, try using your own nand backup as an emunand. Lastly, there are 2 versions of neek, the traditional neek and neek2o. ModMii's default setting is to build neek2o, but IIRC neek2o currently has problems with booting sneek+di. The best place to report problems on this is in the dml or neek2o threads. When it comes to things of this nature, ModMii is basically just the messenger, you want to talk to the real devs behind the project (I'm in touch with them anyways so if they need me to make changes to ModMii I'm sure they'll let me know). Anyways, I know the devs overjoy and obcd are working on fixing sneek+di support in neek2o, so just be patient for a little while... or u can try using the traditional neek in the meantime.
thx for providing the info I asked for, I'll look into your problems. Today seems to be a bug-fixing day. I actually caught a modmii bug personally today that no one else has noticed\reported. Not really a dangerous bug though because the files in question were correctly being reported as invalid. More info on that will be in the changelog for the next update