While hideous blow does have a casting time listed as 1 standard action, and then the description says “As a standard action,” I think you have to read this as a repeat of the casting time. Otherwise, hideous blow would require a standard action to set it up, and then you could attack as a standard action after that, i.e. on another turn unless you have one of the very-rare abilities to take multiple standard actions in a turn. Since hideous blow is utterly atrocious even without that drawback,1 reading it in there would really just make the entire thing completely pointless. Thus, if you use Quicken Spell-like Ability, it ought to affect the casting time—which the “As a standard action,” is merely repeating. So it should affect that too, allowing a swift-action hideous blow attack.
Therefore, since hideous blow just has a casting time—that gets mentioned in its description, but nonetheless—spellblast changing that casting time should be valid, allowing you to combine them. After all, hideous blow is a blast shape and spellblast is an eldritch essence, and they both explicitly mention the possibility of including the other.
Overall though, hideous blow is terrible,1 and it’s particularly terrible with spellblast since a lot of spells are going to include you in the area, so you have to somehow work around that, or limit your spell selection to those spells that either have areas you can direct away from you (e.g. cones) or whose effect naturally ignores or benefits you. Those are some serious drawbacks, on top of an already-awful blast shape.1
- While it’s perfectly valid to wonder and ask how hideous blow works, please know it is never worth taking. It is a terrible trade—massive loss of accuracy for the sake of just one hit of weapon damage. If your weapon damage is good, you’d be far better off with a full-attack than the eldritch blast damage or eldritch essence effect. If your weapon damage is not good, particularly if your weapon damage is poor due to low accuracy, then giving your target what amounts to a massive AC boost by attacking their armored AC instead of touch AC is not remotely worth that small damage. Finally, if you have Dragon Magic, the eldritch glaive blast shape found there is vastly superior—it is still a touch attack, it actually lets you get your iterative attacks (though not any other bonus attacks), it has reach, and it lasts the whole round so you can threaten with it. (Even if you don’t have Dragon Magic, that just means you lack any viable melee warlock options, not that hideous blow is an acceptable replacement.)