Let’s start with the GIRM. While entrance, recessional, offertory and communion processions are addressed in the GIRM, the only mention of a crucifix and candles to be used in a procession is at the entrance. Nevertheless it is common practice, and in fact the custom, that the servers also carry the processional cross and candles when they exit in the recessional.
So, as for the use of processional candles and processional cross as a way to escort the gift-bearers to the altar during the offertory, if it is not specifically prohibited by the GIRM, it could be difficult to make the case that it should not be done.
In answer to your question, from the documents I have studied, it is not “absolutely forbidden to use the processional candles during the offertory.”
Rev. Francis J. Hoffman, JCD (Fr. Rocky) is Executive Director of Relevant Radio. Ordained as a priest for Opus Dei in 1992 by Blessed John Paul II, he holds a doctorate in Canon Law from the Pontifical University of the Holy Cross, an MBA from the University of Notre Dame, and a BA in History from Northwestern University. His Question and Answer column appears in several Catholic newspapers and magazines across the country.