Forensic analysis methods are not scientifically validated in general. AFAIK any forensic evidence is admissible if the the judge decides so. The general standard is that is sounds plausible.
No. The general standard is the Daubert standard (so named because it arose in Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993). The standard is:
Judge is gatekeeper: Under Rule 702, the task of "gatekeeping", or assuring that scientific expert testimony truly proceeds from "scientific knowledge", rests on the trial judge.
Relevance and reliability: This requires the trial judge to ensure that the expert's testimony is "relevant to the task at hand" and that it rests "on a reliable foundation". Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 584-587. Concerns about expert testimony cannot be simply referred to the jury as a question of weight. Furthermore, the admissibility of expert testimony is governed by Rule 104(a), not Rule 104(b); thus, the Judge must find it more likely than not that the expert's methods are reliable and reliably applied to the facts at hand.
Scientific knowledge = scientific method/methodology: A conclusion will qualify as scientific knowledge if the proponent can demonstrate that it is the product of sound "scientific methodology" derived from the scientific method.
Factors relevant: The Court defined "scientific methodology" as the process of formulating hypotheses and then conducting experiments to prove or falsify the hypothesis, and provided a nondispositive, nonexclusive, "flexible" set of "general observations" (i.e. not a "test")  that it considered relevant for establishing the "validity" of scientific testimony:
Empirical testing: whether the theory or technique is falsifiable, refutable, and/or testable.
Whether it has been subjected to peer review and publication.
The known or potential error rate.
The existence and maintenance of standards and controls concerning its operation.
The degree to which the theory and technique is generally accepted by a relevant scientific community.
That's a whole lot more stringent than "sounds plausible" (which is fairly close to the Frye "general acceptance" standard that Daubert replaced).