But I've not found any evidence so far that any of the pioneers denied the person-hood of the Holy Spirit.
U. Smith did -- he wrote:
"respecting this Spirit, the Bible uses expressions which cannot be harmonized with the idea that it is a person like the Father and the Son. Rather it is shown to be a divine influence from them both, the medium which represents their presence and by which they have knowledge and power through all the universe, when not personally present.” {Uriah Smith, Oct 28, 1890, Review and Herald}
On the other hand, EGW wrote:
"Sin could be resisted and overcome only through the mighty agency of the Third Person of the Godhead, who would come with no modified energy, but in the fullness of divine power. DA 671
"We need to realize that the Holy Spirit, who is as much a person as God is a person, is walking through these grounds.--Manuscript 66, 1899
"The Holy Spirit has a personality, else He could not bear witness to our spirits and with our spirits that we are the children of God. He must also be a divine person, else He could not search out the secrets which lie hidden in the mind of God. "For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God."--Manuscript 20, 1906.