I played a bit with this service, today.
I realize I did not follow the instructions [partly because my Armory does not provide compresses private keys only the one that start with 5. So does the BTS client btw when you use wallet_dump_private_key, even though you say it does use compressed ones, maybe internally], anyway with that in mind I used amounts that I really do not care about.
- I dumped the private key, using wallet_dump_private_key, of the active public key of an unregistered BTS account.
- Imported those in the BTC wallet.
-Transferred BTC to the gateway address from there and got the bitBTC.
- Using the GUI sent those bitBTC to metaexchangebtc and got nothing back...
No worries, as I said it was a very small amount, just letting you know how it went.