A few thoughts:
Mesons (real world ones, anyway) are particles bound by the Strong force, so could be affected in theory. However, in practice a meson beam is invisible and launched from a potentially undiscovered source to an undisclosed target at near light speed, so actually focusing the damper node on a group of mesons would be near impossible. Presumably, meson screens interfere passively rather than via an active focus.
Fusion guns have a similar problem of beam speed and as stated above, the damage is thermal not a function of radiation release. Yes, if you focused on the gun itself, you could stop it.
Ships don't carry damper weapons since the weapon range/accuracy is a function of beam separation - they are short range weapons that are unsuited to ship combat.
A pair of dampers in the hold of a starship could theoretically halt a power plant, but only while they were switched on. An overload would not cause permanent damage IMTU, YMMV.
Dampers will only work if they are focused on the target. The target location must be known (where, exactly, is the fusion core in the enemy ship's power plant?) and must be of a targetable size (we're told it can focus on a warhead - say 1m across, but can it focus on the fusion chamber of a FGMP? How big is a 'node'?