No it's linked to each other! It is basically just another front end to the Steem Blockchain....
If you post via Dtube you actually make a Steem Post with an already included video...
They take 25% of your money from a post in service of providing the servers and storing your video files...
I personally think that is not too much but I think they should cap this to certain amount ...
Greets! :)
Thanks for letting me know. Sounds great! Keep up the good work :)