For chemical reactions occurring in the interstellar medium, which involve metal-ions, will the metal ions be solvated or not?
Per Wikipedia, the upper bound on the particle density in the interstellar medium is approximately $\pu{E6}$ molecules per cubic centimeter, in "cool, dense regions."

In the context of terrestrial aqueous solvation, where the concentration of water is approximately $\pu{55M}$, the particle density is on the order of $\pu{3.3E22}$.

So, even if every single particle in the vicinity of a metal ion in the ISM were a water molecule, the ISM would be roughly $\pu{E18}$-fold more dilute in neighboring water molecules as compared to aqueous solution.

No, metal ions in the interstellar medium will never be solvated.

Note that this does not imply that it is impossible for aquo-complexes of transition metal ions to occur in the ISM, given their significant affinity for ligands in the first coordination shell and for the appreciable organizing influence (thanks, MaxW!) such ions have on more distant coordination shells. It's just highly improbable that one would find a metal ion associated with a sufficiently statistically large number of water molecules to be considered solvated.



Further, to address the portion of the question about thermodynamic equilibrium: I don't think that's a particularly significant factor, no. On Earth, it's frequently the case that ions are solvated but not in thermodynamic equilibrium: the proton gradient that is sustained in the aqueous milieu of biological organisms to drive ATP synthase is one of the most significant examples that comes to mind. Thus, an absence of thermodynamic equilibrium does not necessarily entail a lack of solvation.