Radical though this may be, I think explicit statements that they survived trump 'strong implications'. In Corax's case, it's even quite well documented what he did after the Drop Site Massacre. It's rather important - the Emperor told him to rebuild the Raven Guard, he authorised the use of a dangerous, experimental technique to clone Space Marines, was tormented by the guilt of knowing he'd created thousands of monsters as a side effect, killed them all personally, prayed for a year and a day, and in the end headed off into the Eye of Terror. It strikes me as being, on the whole, stronger evidence than a mere implication in
Fulgrim. Vulkan is less well documented, but he's been repeatedly referred to as siding with Dorn in the codex dispute, and the Salamanders themselves believe he's still alive and will return. It's unlikely they'd believe that if they knew he died.
All
Fulgrim says is this -
[p. 482]
Ferrus Manus watched in mute horror as he saw a storm of fire engulf Corax, and a titanic explosion mushroom skyward from where Vulkan stood in astonished outrage at what was happening.
[p. 494]
Of Vulkan there was no sign, his warriors cut off and surrounded by the Night Lords and Alpha Legion.
I don't seem to see any other mention of them after the massacre begins. On a quick flick through Horus never seems to talk about them, nor is their absence specifically noted other than the quote I just posted.
Fulgrim never says that they die, and makes specific mention of the fact that a number of Raven Guard, Iron Hands, and Salamanders escaped. Judging from what we know from other sources, it seems obvious to me that they survived. Nothing in
Fulgrim necessitates that they're dead, and as they're both noted as having done things after the Heresy that would be rather difficult for dead people to do, I'd make the assumption, radical though it may be, that they survived.
Then again, I like to think Ferrus Manus survived and Fulgrim wasn't possessed by a daemon, but we all have our little conceits.
