To judge by the website you gave, apparently this is a rather specialized term which can't really be translated.

"Draft dodger" or "draft evader" won't do --even though these guys did, indeed, "dodge" or "evade" the draft-- because what was no doubt involved was somehing much more *active* and, ultimately, dangerous. There was nothing "passive" about Resisting the Nazi occupation of your country, it seems to me.

And, they did more than "dissent" or even "oppose" --these are just too mild terms.

What we are talking about here is a specific aspect (subset) of The Resistance, at least in Luxembourg, and, probably, in other occupied countries.

(Capitalising "the Resistance" gives it something of the status which it deserved, btw, and I've seen that done often when speaking of the French Resistance.)

It seems that "réfractaires" refers to members of the Resistance who chose to fight the Germans in relatively non-violent ways --not by blowing up trains or other sabotage, but by resisting (by what means, one wonders?) the Conscription imposed on the native population.

"...the activities of those who refused conscription and were active in the Resistance..." maybe.