I keep a raw image file with every jpg. Digikam handles this nicely, but the html export does not. Imho it would be nice to select one (or more) type of file that should be exported while others are not. Reproducible: Always
In digiKam 6.4.0 (and earlier versions) you can use the "Search" tab (on the left navigation column) to create a search for a particular Album (file directory) and/or matching specific tags, and selected file type (see within the "Picture Properties" section of the search form, and where it says "File Format" click on "Any" and then change it by selecting just the file types you want to see included in the gallery). Once you've crafted a search which shows only the images of interest, type a name into the box labelled "Save Current Search" (in the Search pane on the left) and then click the diskette icon to save. Your named search will now appear within the "Searches" list, and anything within this list can be selected when you create an HTML gallery. (Select "Albums" on the very first page of the gallery tool, then select the the "Searches" tab and tick/check as many of your saved searches as you want to include in your gallery.) Using saved searches allows you very fine control over what images to include in an HTML gallery. Does this resolve your request?
Marking this as resolved because digiKam has supported this for some time, and because I see that the original reporter is no longer in the CC list.