If the DWSF formation has wording that allows death wing units to arrive turn 1 I think you'd be able to make a case.
If not then it might just b a special situation that's outside of the DWSF's formations arrival rule set.
I had a similar question regarding NSF units and allied drop pods.
Example:
Gk NSF takes a librarian, 2 strike units, and a purgation squad. They then alli in a DA CAD with a librarian, 2 tac squads, and 3 fasts attack drop pods (because reasons).
Everything enters deep strike reserves, with the purgation squad in an allied Drop pod.
Per NSF: units from this formation can roll to enter from deep strike reserves starting turn 1.
Per drop pod assault: Half of the total # of pods auto arrive turn 1, while the rest have to arrive using normal reserves rolls (usually starting to roll turn 2).
Question: Would the GK purgation squad placed in an allied drop pod be able to roll for reserves turn 1 (NSF)? Or would the drop pod assault rule take precedence because technically you are making reserves rolls for the pod only?