Yes, you can delete the videos from Dtube. To do so follow those steps.

1. Login on steemit to the account that was used to post the video on Dtube.
2. Go to the blog section of your account.
3. Click on the Steemit post that shows your Dtube video.
4. On the bottom you will see a Reply, Edit and Delete link. Click on Delete.

This will delete the post on Steemit but also on your Dtube channel.

Take in consideration that the Delete link appear only during a limited amount of time after uploading the video at Dtube.
On old steemit posts, the delete link disappear and you cannot remove it anymore.