Hi Alan
I have to say that I am surprised that you have not found what you are looking for after seven years (?) of searching, as the information is readily available.
Firstly, regarding the Boer War he did not serve – according to the medal roll at least.
For the 1901 and 1911 Irish census anyone living in an institution (including barracks) only recorded their initials. Looking for a JM produces 4-5 in the Dundalk barracks, but all of them were too young to be a Sergeant Instructor.
Your post is a good example of why it is important to link threads together as it was only as I had a few minutes spare that I bothered to check your other posts. And found details off the son born in 1900. Families are recorded in full in the Irish census and here is his wife and two children -
http://www.census.nationalarchives.ie/reels/nai001043824/Notice than he signs the form.
Form H is the form for the men - with the initials. He is not there, but there are two possibilities. The list ends with Lance Corporals, so other forms may have not been transcribed. Or he is actually the WW listed as the Sergt Instructor of Fencing. The form filler may have confused him with the other WW Staff Sergeant a few lines down. Only a guess, and not really important as his service record is online -
http://www.findmypast.co.uk/army-service-records-show-image.action?sdrfnbr=975533018 – so you do not really need his 1901 census form.
Page 10 confirms he is the right man with details of his wife and children’s place/dob.
It also gives his NoK on enlistment – father and seven siblings with (o) being older and (y) being younger.
He was born in Birmingham and originally in the infantry. He did go to SA but only after the Boer War ended.
Ken