Yes, the dtds for the collections listed in IndexCat™ are available at:

Index-Catalogue collection dtd -  https://www.nlm.nih.gov/databases/dtd/nlmindexcataloguerecordset_130401.dtd

eTKeVK2 collection dtd - https://www.nlm.nih.gov/databases/dtd/nlmetkevk2recordset_130401.dtd