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