EDIT: Here are the results after several pages of discussion, with quotes of the relevant rules:
Auto-hit weapons can't hit Zooming Flyers unless they have the Skyfire special rule.
Auto-hit weapons on flyers can choose to use Skyfire each turn to be able to hit Zooming Flyers, but if they do then they can't hit non-flyer units unless they also have the Interceptor rule.
The Deathstrike Missile is a blast weapon according to the Errata, so it can never hit Zooming Flyers.
Page 81: "shots resolved at a Zooming Flyer can only be resolved as snap shots (unless the model or weapon has the Skyfire special rule)" (bold added for emphasis)
Page 81, top left: "Flyers can choose whether or not to use the Skyfire special rule at the start of each shooting phase. They don't have to use the Skyfire special rule, but if they do, all weapons they fire that turn are treated as having the Skyfire special rule."
Page 42: (SKYFIRE) "A model with this special rule (...) fires using it's normal Ballistic Skill when shooting at flyers (...) Unless it also has the Interceptor special rule, it can only fire Snap Shots against other targets."
Page 13: "any shooting attack that does not use a ballistic skill (...) cannot be "fired" as a Snap Shot" (quotation marks on "fired" direct from the rulebook).
Below is my original post, for legacy reasons
Take things like the Necron's Death Ray or the Eldar's D-Cannon. Both of these weapons don't roll to hit, but instead draw a line and automatically hit any models it touches. So, can you use these weapons against zooming flyers?
I've only just read the 6th edition rulebook and may be missing something, but I don't see why not (probably I just skipped some important rule).