You are probably referring to RALPH Woodrow a famous Evangelical preacher who once espoused the opinions of Hislop from his book the "Two Babylons" but who later retracted his statements. As far as I know he has no connection to the Watchtower.
I was around in the 50s, 60s and 70s when the Watchtower regularly quoted Hislop's book, but only selectively and with scant regard for Hislop's thesis. It was obvious that the writers of Watchtower material had not actually taken the trouble to read the work. This is not unusual since it is weighty, often contradictory, mixing fact with opinion, and largely bigotted in its conclusions.
As far as I can recall, the only occasions when the Watchtower quoted Hislop were to prove:
1. That the Cross was pagan
[Which is something that Hislop did not conclude. His stated opinion was that the CRUCIFIX of the RCs was. The RCs, like the Watchtower, still depict Christ on his instrument of death, revealing a theology that subscribes to the RC position that the redemptive work of Christ is still operative and that devotees must somehow accomplish works to acquire the distinctive formula for salvation.
His point, now considered more opinionated than factual, was that the RC Crucifix was derived from the Egyptian Crux Ansata, which was portrayed as a a T form with a round top, evidently depicting someone's head. It did not. It was merely a handle. The Egyptian crux also showed two lines extending from the upright post to the arms of the T thus showing someoine's arms. This to Hislop was a picture of Christ still on the cross.
Evangelicals on the other hand believe explicitly that when Jesus said "It is finished" that His work was complete. Thus they always display an EMPTY Cross. Hislop's point was that the RCs, and not Christians wholesale were "pagan".
The inability to distinguish the two was a point of ignorance on the part of Watchtower writers and not one of agreement]
2. That the Trinity was "pagan"
[Again, this is not true, since Hislop was himself a Trinitarian. His point, when carefully read, would show that he was arguing that the DEPICTIONS of the Trinity such as triangles, three headed gods, arcs, curlicues, and so on, were Egyptian in Origin, although Hislop was probably rather far fetched in his conclusions. ]
3. That Christmas Day was "pagan":
[Oddly enough Hislop did not use the Roman Saturnalia to prove this point, which would have had more historical value as a point of argument. He chose rather to stress the point that Nimrod, the great bogey man of Watchtower myth, was born on this day. As later scholars would show this is an idiosyncratic opinion which has no historical basis whatever.]
The Watchtower pulled any further reference to Hislop sometime in the late 70s, probably because someone may have pointed out that their references to him, and their quotes of him were ill considered.