HDR and exposure fusion (as done by a tool like enfuse) are two different ways of attacking the same problem, but exposure fusion is NOT an HDR technique and does not require HDR file formats or tone mapping.
Enfuse's main algorithm does not involve remapping tones along a larger dynamic range, but selects and weights values from the original pixel data of member images, based upon three criteria. From the enfuse website:
The basic idea is that pixels in the input images are weighted according to qualities
such as proper exposure, good contrast, and high saturation. These weights determine how much a given pixel will contribute to the final image. A Burt & Adelson multiresolution spline blender is used to combine the images according to the weights. The multiresolution blending ensures that transitions between regions where different images contribute more heavily are difficult to see.
Instead of mapping out all the tones in the member images along a high dynamic range, and then tonemapping back down to an LDR format, weighted averaging is done on the original member pixel values to create the final image pixel values. Essentially every value in the final image is going to be within the range of the original member image values, not necessarily the result you get with HDR and tonemapping, which can manipulate the luminance and saturation of pixels outside the original range.
In more manual methods of exposure fusion, simple masking allows for pixel selection from member images into the final image--again, no mapping to an HDR file values or tonemapping is required. You can also think of enfuse as masking and selecting at the individual pixel level.