Hi,
I've come across that line previously but never found a connection to my in-laws family.
I have a few notes on them:
David NB Haggart 1895 Laurencekirk
Robert Haggart b6 Sep 1872 m Annie Bruce
Robert Inglis Haggart bc1840 - d29 May 1900 - m1862 Kinross, Margaret Nicoll
The death record for Robert showed parents as David Haggart / Janet Crockett.
The marriage record showed parents as David Haggart / Mary Crocket
I never located birth for Robert
There was a marriage in Alyth in 1825 between a David Haggard and Mary Crockat
I found no marriage to a Janet
Other children to David / Mary (from Family Search / LDS).... David 1826, Mary 1828, Jean 1831, William 1835, James 1837.
David and Mary would appear to be correct names as this is backed up by the names in the 1841 and 1851 census records in Markinch:
1841
David Haggart 41
Mary Haggart 35
David Haggart 14
Mary Haggart 12
Jean Haggart 10
Willm B Haggart 5
John Haggart 3
James Haggart 3
Robert I Haggart 1
1851
David Haggart 50
Mary Haggart 48
David Haggart 24
Mary Haggart 22
Jane Haggart 20
John Haggart 13
James Haggart 13
Robert Haggart 11
My notes are sketchy after that and I seem to have abandoned the search, having decided that there was no connection at that time to my in-laws. There could of course be a more distant connection.
Variations I've come across have been Hag(g)art, Hag(g)ard, Heggart(y), Hoggart(y), Hog(g)arth and a few other obscure spellings.
That's all I have but I hope it helps.
For reference, my in-laws line is:
Mother in law (living)
David Walker Haggart b1872 d1955 m(1) Eliz Bowie m(2) Agnes Wardrop Hamilton
Andrew Haggart b1839 Abernethy m Helen Milly
William Haggart b1793 Abernethy m Mary Walker
John Haggart bc1770 m Margaret White