I don't think we should be worried if our application gets denied

Unless you have some pretty serious stuff on your record.

Doesn't this memo state that the people who still qualify for the DA won't be prosecuted and deported?

I think this just states that you can apply for a work permit while they work on the D.A.

According to the DHS website, only those who apply that have committed serious crimes, are felons, etc. will be handed over to ICE for removal.