There is an option when exporting DDP to use only the selected set. So I would enable DDP on all features of the index layer, then create my selection, then export.
In the UI, go to File --> ExportMap --> Select PDF --> Pages Tab - check Selection (optionally you can show selection)
In arcpy, the parameters are:
exportToPDF (out_pdf, {page_range_type}, {page_range_string}, {multiple_files}, {resolution}, {image_quality}, {colorspace}, {compress_vectors}, {image_compression}, {picture_symbol}, {convert_markers}, {embed_fonts}, {layers_attributes}, {georef_info}, {jpeg_compression_quality}, {show_selection_symbology})
Set page_range_type = "SELECTION", optionally, set show_selection_symbology=True
Jeff