Are scientists often in a position to provide advice with holistic value? I'm usually quite skeptical of advice like this when it comes from someone who is laser focused on a specific domain.
When Jan Smuts coined the term [1], he was unfortunately at a too immature scientific stage to pave the way for a careful and thorough academic field of study. Moreover, due to his political full time occupation he never got to the stage of forming a precise idea of what he wanted his book to be about. I personally think that his book should have been a fine ecological assessment rather that a somewhat philosophical treatise.
But to answer your question, I think absolutely they are able to provide such advice, with the limitation that it would be holistic in a small and specific context. For example, recently a scientist commented to me that wildebeests being replaced by cattle (wildebeests are not endangered) does actually not negatively affect the microbial biodiversity. But the comment was about specific biomes in a specific area. When you move from grasslands to bushveld, then cattle have a side effect of stimulating the growth of sekelbos [2].
The way I take it, Holism and Evolution was Smuts's response to Darwin's work and in a more ideal world, Smuts's work could have been a nice addition to On the Origin of Species. Smuts's main observation was that the whole is often "greater than the sums of parts". I lament the lost opportunity, but this kind of idea even occurs in pure mathematics. That is why you take transitive closure when you take the union of two or more equivalence relations.
In the ecological context, what he essentially meant is that two species in isolation from each other, as a whole, has a smaller ecological impact than those same two species living interactively.
I have not read his book, but I understand it to be (in the scientific formulation sense) unfinished.
[1] https://en.wikipedia.org/wiki/Holism, first sentence [2] https://af.wikipedia.org/wiki/Sekelbos