According to Wiki
Adjunct(grammar),
an adjunct is an optional
part of a sentence, clause, or phrase that, if removed or discarded, will not otherwise affect the remainder of the sentence.
In the case that "Useful as these tools may be" be concessive adjunct and discarded, the sentence would be "
they offer a cure in an area where the first concern should be prevention".
This is obviously not a complete sentence since antecedent is omitted, thus I don't think it's a concessive adjunct.
I favor TheParser's answer.