I've never heard it before, but it appears to be a (playful?) variation of deluder, one who deludes or tricks another. The th/d/dh appear to be different attempts at transliteration of dialect. Here's all the sources I found using delutherer and deluderer, and are all of Irish origin.
The Dublin University Magazine (1855):
"Was the wise woman prosecuted?" we inquired.
"She the, deluderer," replied Dan. "Likely enough. Do you think the wise woman would let herself be nabbed that way.
Captain O'Shaughnessy's sporting career by J.R. O'Flanagan (1873):
The last is true at all events, I go bail,' said Father Ned ; ' but, you deluderer, what call have you to a parishioner of mine ?' " ' You may well be proud of your parishioner/ retorted the other. ' You know he hasn't been inside the chapel for a ...
The Athenæum: A Journal of Literature, Science, the Fine Arts, ...: Volume 1 (1891):
It is not the first time he has shown a grasp of Irish character; and Tim Daly, the philanthropist's factorum, patriot, lover, schemer, “delutherer,” is as fine a Paddy as ever kissed the blarney stone.
Humours of Irish Life includes "The First Lord Liftinant" By Percy French (1854 – 1920):
“Faith, I can’t,” says the Queen. “Hould on till I draw the
bed-curtains. Come in now,” says she, “and say your say, for I can’t
have you stoppin’ long—you young Lutharian.”
“Bedad, yer Majesty,” says Essex, droppin’ on his knees before her
(the delutherer he was), “small blame to me if I am a Lutharian, for
you have a face on you that would charm a bird off a bush.”
The Conservative: Volume 3 (1900):
... for he must fall upon the evil fame and days of the false prophet, and "the deluderer of men," as Father Tom called the pope, while enjoying that fine old Irish whiskey which he carried with him to Rome — that famous distillation which, new to His Holiness, so overcame him with its aroma at the very start, ...
Titanic survivor: the newly discovered memoirs of Violet Jessop by Violet Jessop and John Maxtone-Graham (2004) describes "the good old Irish doctor":
"Sure, haven't I worn all the knees out of me pants proposing to ladies and sure they won't have anything to do with me at all."
Meanwhile our eyes wandered round his room adorned with silver framed photographs of some of the most beautiful and talented women of both hemispheres. He was our dear "deluderer."
The Spell : A Comedy in One Act (1922) by Bernard Duffy:
Mrs. Heraty. You did, and it was that, and
the like of it, that put the commether on me.
You drew me from me home with your
Mrs. Heraty. Don't listen to her ; she's a
Tales of the Little Sisters of Saint Francis by Shaw Desmond (1929):
... elephants' tusks, for Brother Jerry could get anything to grow. This was the laddo who would be showin' himself coy around the corner of the cattleshed and I solderin' away and mindin' me own business, wid that mermaid delutherer lookin' ...
Another spelling of the noun is deludherer or deludher. Sometimes the deludher is a verb, and perhaps this led to the extra -er for the noun. Some examples:
Legends and stories of Ireland (1827) by Samuel Lover includes this from "The Burial of the Tithe":
Sometimes when the girl he wanted to be sweet on was seated at the back of the car, this relieved the horse from the additional burthen of his driver, the clane boy would leave the horse's head and fall in the rear to deludher the craythur, depending on an occasional " hup" or " wo" for the guidance of the baste, when a too near proximity to the dyke by the road side warned him of the necessity of his interference.
Billy Malowney’s Taste of Love and Glory (1850) from “The Purcell Papers” by Joseph Sheridan Le Fanu:
Well, Billy Malowney follied her down the boreen, to try could he deludher her back again; but, if she was bitther before, she gave it to him in airnest when she got him alone to herself, and to that degree that he wished her safe home, short and sulky enough, an’ walked back again, as mad as the devil himself, to the wake, to pay respect to poor Tom Dundon.
Cedar Creek: from the shanty to the settlement : a tale of ... (1863) by Elizabeth Hely Walshe:
... grinned and jabbered in patois (old as the time of Henri Quatre) among themselves.
"The deludherer!" muttered Andy. " He'd coax a bird off a three wid his silver tongue. An' he must come betune my own gintlemen an' their frind — the old schamer!"
The life and adventures, songs, services, and speeches of Private Miles O'Reilly (1864) by Charles Graham Halpine:
Till time lets pass his empty glass,
Lord Pam — [Avic! ye ould deludherer, that
ought to know betther, and that does know betther, but can't
help yourself aroon]—
Lord Pam, 'tis you're my glory !
There's more in Google Books, and all appear to be Irish.