There is a valiant and ongoing effort by Mrs. Fleming to index the marriages on CityArk with most of Dartford RD completed and starts on Medway and Hollingbourne RDs courtesy of Allan Beattie. This link will take you to the index of the registration districts:

In the sections that have been indexed she has included a surname index so that if there is not a name of interest in the index one can rule that area out very quickly as a possible place for a marriage of an ancestor.

A link to a completed index of a section will, when clicked on, open up a PDF file where the events have been more fully indexed. This index is chronological so you will have to use the "Search" facility within PDF to locate a particular person, unless of course, you know the date of the marriage.

If you find a marriage in the PDF index, you will see that URLs in the form of TinyURLs have been included to the left of a set of entries. If you click on that TinyURL you will be taken directly to the page on which the marriage appears, in the CityArk registers.

I hope this answers your question and perhaps the marriage index can help you as if a marriage took place in a particular area there is the distinct possibility that the couple stayed in that area for part of their married life and you may find children baptised and buried in the same register.