let us take a God, say, Apam Napat.
If some scripture says Apam Napat is supreme (Rig Veda talks about his Paramam Padam) - then it can simply be argued that Apam Napat is a name of the sectarian supreme God.
So with respect to any scripture that glorifies any entity as Brahman, it can be said that that entity is that sect's supreme God in one of three ways (all names of Brahman mean only that God, that God is the Antaryami of everybody, all names are only attributes and can be taken to mean that sect's God).
With this understanding, no Tamasic or Rajasic deity can be praised as Brahman from the standpoint of this sect.
How can there be Tamasic or Rajasic scriptures for such sects?
EDIT: The ideal answer should cite from canonical Sanskrit scripture or provide examples of real sects and their teachings in Sanskrit or other languages.