I've got the XDM 5.25, and the front sight is the same as my XDM 3.8 Compact, so I would think any XDM tritium front sight would work on the 5.25, and you would just install it by drifting it into place.
The rear sight is really not compatible with anything, being adjustable and all, but maybe you could paint the rear of the blade with some luminescent paint? Just thinking out loud here... I know a lot of pistols only do a tritium front sight anyway, as many people prefer a flat black face on the rear. I do like that on the 5.25, you can rack the slide with the rear sight if you had to in an extreme case where you only had one hand free - I don't like the Novak style rear sight on my XDM Compact for that reason - the slope of the Novak style sight prevents using it as a surface to rack the slide against a belt, table, whatever.
EDIT: just figured out that there is a slight difference between the front sight on the 3.8 and 4.5 versus the 5.25. See post below...