My impression is that, while De Smet in 1953 defended the thesis that Sankara was a srutivadin, and while he discovered in him a theory of analogy (laksana) that corresponded closely to the intrinsic analogy of Aquinas, he had not as yet come clearly to the affirmation that Sankara was not an acosmist. This needs to be confirmed by a reading of the text of his dissertation.
By 1964/68 (his article for Religious Hinduism) - and perhaps already in 1958 (the first edition of this article) - he is certainly maintaining that Sankara is not an acosmist. The notes (Guidelines in Indian Philosophy), which bear a 1968 date on the front page, also bear this out quite abundantly.
It might be another interesting study to find out the position of the Calcutta School of Catholic Indologists on the matter. What did Johanns and Dandoy think? Pessein? Etc.