That framework became the objection to them.
The Singh Sabha movement from the 1870s split over precisely this question. Its Sanatan wing, which held that Sikhism stands within the broader Indian religious inheritance, supported the Nirmala scholars and used their work. Its Tat Khalsa wing, which held that Sikhism is a distinct revelation owing nothing to Vedanta and requiring no Sanskrit apparatus, condemned it. The Tat Khalsa position prevailed, and the consequence for the Nirmalas was that the exegetical tradition on which Sikh theology had rested for a century and a half was recategorised as contamination.
The order fared better than the Udasis in the disputes of the 1920s, being closer to Khalsa practice, and it retains its akhara, its place in the great pilgrimage gatherings, and a body of students. There is no credible figure for its size.
What the Nirmalas represent is a question the tradition has answered and could have answered differently. Is Sikh scripture best read through the philosophical vocabulary of the world it was composed in, or does reading it that way subordinate it to a system it was written against? Guru Nanak used the language of his surroundings and rejected a great deal of what that language carried. Where exactly the line falls between using a vocabulary and adopting a doctrine is not obvious, and the modern consensus settled it in one direction by a movement's decision rather than by demonstration. The Nirmalas are what the other answer looked like.