I always figured with Gabriel it was something like, Since he drinks blood, when he chomps on a neck, he gets all his mouth chin and upper chest covered in blood, so it's just for convenience. So he doesn't stain his pretty outfit or something along those lines. I like to think that practically every pore on a Vampire absorbs blood, which is why when Drac and Alucard drink blood, the bloody mess on their face fades away after a few seconds.
As for Alucard, i suppose Since he was his son, He gave him some similarly designed armor that follows similar conventions to his own, while still retaining Trevor's own outfit style stuff.
I'm curious as to why he didn't think his Son would revive as a Vampire. I guess he didnt know his blood could revive and turn someone after they were dead.
And to be fair, it DID take quite a long while for Trevor to resurrect as Alucard.
By the way, i was thinking- LoS Dracula... is really the very first Castlevania incarnation of the character to ever actually factor in the Dragon aspect.
The real life Vlad was part of the Order of the Dragon. Which is why he's called Dracula. His father was Dracul, he is Dracula, son of the Dragon.
Other CV games never really delve into that. he just sort of renames himself Vlad Tepes and calls himself Dracula for no other reason than because he's Dracula.
LoS Dracula legot goes the full mile, calling himself Dracul- not Dracula, and often referencing himself as "The Dragon, Dracul"
With the people calling him Dracula, likely because in their eyes, Satan would be the Dragon, and Dracula evil enough to be the spawn of satan or some thing like that.