Thanks, Alan. I appreciate the kind words.
As Bart says, HDR with film scans is a bit more difficult. Ideally, for best results, HDR programs want linear data. Even if you send gamma encoded TIFF files to an HDR program, the program should read the embedded gamma curve and reverse it to get back to linear data. Even if you shoot JPEG, while JPEGs aren't linear they only have the gamma encoding of the embedded colour profile to worry about. With film, you've got the natural tone curve of the film plus the gamma encoding from the scan and embedding of the colour profile.
Some scanning software can output linear 'RAW' scans. VueScan can, as Bart notes as can Silverfast (not sure about any others). This will eliminate the colour profile gamma encoding but not the natural tone curve of the film. Photomatix has a process that will attempt to reverse-engineer a tone curve that they suggest using for film scans. It's only available in Batch mode; however. Which is OK, you can use Batch mode on a single set of files.
Unlike digital where multiple processing of a single RAW file into 3 output files at different exposure settings won't have any benefit for HDR merging, with film it is possible to delve deeper into shadows and possibly recover some highlights by adjusting the scan exposure (at the time of scanning, not afteward). Not quite as good as having 3 separate film scans but still some benefit compared to digital RAW files.
I've tried the multiple scan method for HDR on some old film images with mixed results. None that I've been really pleased with but I haven't tried it in several years either so improvements in scanning software, HDR software and my own knowledge set may mean I could get better results today. Bracketing for HDR with film can get pretty expensive too. A scanner/software combination with multi-scan functionality that can do multiple scans of the same film frame at different exposure levels will help pull a bit more shadow detail than sometimes a straight, single scan can.
If the goal is simply expanded brightness range and GND filters aren't possible or aren't sufficient, then exposure fusion/exposure blending (either automated or manual) is the better approach, I think. Photomatix does have an exposure fusion utility. SNS-HDR, while having tonemapping ability, is an exposure fusion tool. There're also Enfuse & TuFuse which are good quality fusion programs.