What a fascinating google search you sent me on! Here's the only reference I found on that database, ZWT - 1916 VOL. XXXVII AUGUST 15 NO. 16, A.D. 1916--A.M. 6044:
OBJECTORS SING, "STAND UP, STAND UP FOR JESUS!" DEAR BROTHER RUSSELL:--
We read with special delight this morning in June 1 WATCH TOWER your recapitulation of those wonderful events in the years when the Lord graciously provided "line upon line" of the basis of what we now know as the Truth . It does our hearts good to ponder over these things and examine our foundations again and find they are rock-bed ones and immovable. As we read the details we take fresh encouragement in the hope that the Lord is yet going to show further developments through the same channel. We trust so.
A new phase of experience has been entered into in this country--an experience specially trying to the younger members of the "Body," many of whom are undergoing terms of imprisonment with more or less of hard labor. Many a mother's heart is wrung with the severity with which her loved lads are treated; yet we hear from these same lads glowing accounts of the goodness and faithfulness of our Father and barely a hint of complaint, although we know they are sorely tried. One contingent (a day or two since,
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numbering about forty) were marched away from the camp where they had been detained pending court-martial, to prison. There were only four or five of our brethren among these, the remainder being moral objectors, and our brethren describe them as a splendid lot of fellows. Educated and professional men along with honest, hard toilers were thus thrown together, and on one point wholly sympathetic and determined. As they passed through the Camp they unitedly sang, "Stand up, stand up for Jesus!" It was almost dramatic,
"And e'en the ranks of Tuscany
Could scarce forbear to cheer."
In fact, some of the regular soldiers did cheer them and numbers, we are told, confessed admiration. Many STUDIES have been gotten out, too, among warders, jailers, constables, officers and men, as a result of contact with these few "voices in the wilderness." To see the courage and fealty exhibited by these young brethren causes us a deal of heart-searching and magnifies intensely our own failures and constant slips. While they have opportunities for service thrust on them, we seem to have a barren existence and a diminished activity. We are praying that the Lord may show His hand and thus lead us more fully than ever into the light. We are ever with you in Spirit.
Yours in the dear Lord, F. GUARD, SR.-- London.
It would seem far more likely that the Bible Students of those days had no qualms using Christendom's hymns if the moment suited. [Edited to add] OK, I read that article again, and if I am reading right, the entire contingent of conscientious objectors , five of the forty being Bible Students, sang together.