No, we have no relation with Bytecoin's devs. Dashcoin a 1:1 Bytecoin copy. It probably stay as such unless Dashcoin becomes so big we can afford full time developers better than Bytecoin's.
Bytecoin is launched within small set of people (mostly related to devs computer specialists). Dashcoin has an open launch - it is for everyone.

The reason we made Dashcoin is because:
1. Currently all clones of Bytecoin have huge difficulty of maintaining their base code.
2. The leader's strategy is based on creating negative image of everyone else. This does not talk good about the leader. Not telling their community don't do good things also.

The GUI wallet will be made 3rd party. Currently I have knowledge that Minergate's owner is willing to make one, no timeframe about that. GUIs wallets and web wallets are huge niche and 3rd parties should realise that.
Also Bytecoin maybe will integrate GUI in their core code soon. We are preparing for a move like that.
By looking at the other coins' GUI, it's not a big disadvantage that we don't have one. Their GUIs start the daemon and simplewallet, which should not happen in a production version of a GUI.