"We don't need gurus any more." Amen to that. I've been singing traditional songs now for nearly 60 years, longer if we include those passed down in my family, and while I'm pretty certain I will have picked up some style and nuances along the way I'm not conscious of any. I know of no-one personally, other than a passing acquaintance with Sandra Kerr, who was part of any passing on of traditional style in a teaching situation. I've come across workshops on singing in general, to improve vocal strength, endurance and breathing, but haven't felt the need to participate.
I have also listened to many traditional singers and although one could perhaps detect a local style where there was a strong tradition these styles varied enormously from region to region and in some cases from singer to singer.
Singers generally adapt to prevailing circumstances, e.g., chanteymen sang in a high-pitched well-projected style for obvious reasons, likewise it has been found that recordings from WWI and earlier, male singers also sang in a high register to project more (No PA in those days).