What is the difference between Leloir and Non-Leloir glucosyl transferases?
LeLoir glucosyltransferases use uridine-diphosphate (UDP) 'activated' sugars as substrate, for example UDP-glucose, where 'LeLoir' refers to the LeLoir pathway, the metabolic pathway that inter-converts glucose and galactose (or, more strictly, the inter-conversion of UDP-glucose and UDP-galactose)
Non-LeLoir glucosyltranserases use sucrose as substrate and do not require the sugar to be be conjugated to UDP (or to be 'activated' in any way), and as such are very useful in the biotechnology industry.
See
A new pathway for the synthesis of oligosaccharides by the use of non-Leloir glycosyltransferases)

LeLoir was an eminent Argentinian biochemist.
For the enzymes of the LeLoir pathway,
The Leloir pathway: a mechanistic imperative for three enzymes to change the stereochemical configuration of a single carbon in galactose
by Perry A Frey is IMO definitive (and the pdf is freely available).
(Glucose and galactose are epimers: they differ only by the configuratation at C4. A key enzyme of the LeLoir pathway is UDP-glucose 4-epimerase, which contains a tightly bound NAD(+) and epimerization proceeds by oxidation/reduction (strictly, hydride abstraction/addition) at C-4, where the tightly bound NAD(+) is transiently reduced during catalysis: ie, NAD acts a (transient) hydride 'repository'! To the best of my knowledge, no enzyme has ever been found that directly catalyses the epimerization of glucose to galactose (although there appears to be no thermodynamic reason why this is not possible): the sugar must be conjugated to UDP in order to be a substrate for UDP-glucose 4-epimerase)