Dtube account is tied to Dtube's blockchain. They now has dual login, Steem and Dtube. Dtube account is compulsory and Steem is only required if you want to automatically post your video to Steem.

Here's tutorial for claiming your @dtube account with your Steem account:
https://steempeak.com/steem/@dtube/dtube-coin-airdrop-claim-your-account-now-with-your-steem-username

#sbi-skip