Mice skating on thin lice...
To be honest, that's a hard question to answer because I don't sound like any singer that I've ever heard, no singer I've ever heard sounds like me and I long, long ago gave up the notion of modelling myself on this, that or the other singer. In addition, there are hundreds of singers that I like and more specifically, particular performances from different ages that I like. For instance, I like the different strands of 'Englishness' that came in the vocals of Mick Jagger, George Harrison, Ray Davies and Syd Barrett in the mid to late 60s and Ian Gillan, the guys from Wishbone Ash, Lemmy and Johnny Rotten in the 70s. But that's only a tiny blip; I love the cool rap/drawl of Gil Scott Heron, the intelligent passion of early to late 70s Stevie Wonder, the sarcsam of T.Bone Burnett, Larry Norman and Bon Scott, the melismatic meanderings of a million gospel and soul singers (ranging from Gladys Knight, Roberta Flack, Diana Ross to Erykah Badu, Des'ree and Marybelle); the Gaelic earnestness of many Irish folkies, I like the hippy whimsy of Melanie, the low level whispered tunefulness of Suzanne Vega and Joan Armatrading.......I could go on for ever and a day and bore everyone to distraction. Suffice it to say, if I like a performance of a vocalist, in some bizarre way I'll hat-check that into my shamelessly eclectic file of what can be done, vocally. But I won't sound like any of it !
There are also, paradoxically tons of vocalists with a unique twist that have pretty much had zero influence as far as singing goes. Maybe it's difficult to separate actually liking a vocalist/vocal from somehow being influenced by such.
In terms of backing and harmony vocals, as 'ten-a-penny' superb as church, gospel, soul/R&B, Hollies, Beach boy, Byrds, Crosby-Stills-Nash-y types are, my main peggers have been those bands that used such but weren't noted for them - The Stones did some outrageously good backing vocals on stuff like "Dandelion" and "We love you", the Kinks, the Floyd and mid to late 60s the Who and early 70s Wishbone Ash. Being so limited in their vocals, they really had to push for something useable and in my view ended up pushing the envelope.
And that's just me. Any of my friends that sing on my stuff bring with them a whole host of influences and styles, many of which I'm not aware of coz to me, they just sound like them.