That is a case of subject/verb inversion called "élaborative". It is mostly found when the subject is long.
Here we have a particularly long subject:
Vinrent s'y ajouter les indemnités qui accompagnèrent la signature des traités d'Étapes (1492), de Boulogne (1497) ou de Tournais (1514), par lesquels les deux premiers souverains Tudor conclurent les « chevauchées » françaises entreprises dans le plus pur style de la guerre de Cent Ans.
With a subject comprising two subordinate clauses the inversion comes naturally in this case. We must also notice that it is not only a subject/verb inversion since the object pronoun y also precedes the subject of the verb. Let's remark as well that the relative clause (qui accompagnèrent...) cannot be separated from indemnités. Had the subject come first we might have lost track of what y was for (i.e reprise des activités).
On Termium Plus you will find more about the subject/verb inversion in affirmative sentences.
I haven't answered that part of the question: "Is it only employed with verbs being used impersonally?" because I do not really understand what you mean since the verb is not used impersonally here. We can have subject verb inversions with impersonal verbs but I do not think they would be of the same nature/purpose.