I find Stephen Gaugroger'saccount of the philosophical criticism of the Enlightenment, and the legacy of the positivism-lebensphilosophie and scientism and romanticism divide it bequeathed, puzzling. Gaukroger says:

The European Enlightenment is generally seen as a formative event in Western modernity, replacing religion, superstition, and absolutist monarchy with reason and democracy. Yet since the middle of the 20th century the shift of values that the Enlightment apparently brought with it has been increasingly questioned. In a 1946 essay, influential German social theorist Max Horkheimer complained of ‘the collapse of a large part of the intellectual foundation of our civilisation’. For Horkheimer, the collapse was due to ‘technical and scientific progress’, which he traced back to the Enlightenment, and above all to what he identified as the ‘self-destructive tendency of Reason’ characterising the Enlightenment mentality.

Gaugroger's remarks are made in a review of Peter Reill in Vitalizing Nature in the Enlightenment, which explores the traditional contrast between Enlightenment mechanism and Romantic vitalism.The above paragraph makes Horkheimer into a romantic who is part of a revolt against science in modernity, rather than critiquing a particular conception of scientific reason--an instrumental reason. The subject-centered reason of the Enlightenment has deteriorated into an instrumental reason. On this understanding reason cannot set goalsand c values cannot evaluate standards; it is purely instrumental in fulfilling given functions. The strength of subjective reason is its be the ability to calculate probabilities and thereby to co-ordinate the means with a given end. It has
become a mere tool to efficiently produce certain ends.

Horkheimer is not criticizing sceince or reason as such, but just the instrumentalized understanding of it.Nor is
Horkheimer anti-science. We do have a Frankfurt School conception of critical social theory to which Horkheimer contributed. This was counterposed to those social sciences that attempted to piggyback on the success of the natural sciences.

Was Horkheimer a vitalist then?

Nietzsche was, but Horkheimer? I cannot recall much on that in the Eclipse of Reason when I read it many years ago. It was not all that concerned with the ontology or metaphysics of the natural sciences.

Western Marxism was influenced by romantic Lebensphilosophie I guess it all depends on Horkheimer's understanding of the materialism, lebensphilosophie and irrationalism of the 19th century. Vitalism places the emphasis on life itself, or rather, the actual flow of life itself. Historically, vitalism stems from the romanticism of the 19th century, begins the 20th century as a right-wing philosophy, and during the late 20th century becomes a left-wing philosophy as well.