Naphtha is usually a mixture of aliphatic hydrocarbons with around 5-8 carbons, like pentane, hexane, heptane, octane, and their isomers. Heptane should be more or less the same to use as naphtha. I think you could basically consider them equivalent.
Maybe naphtha, depending on what hydrocarbons are in the mix, will dissolve DMT a little better but maybe also it will dissolve impurities a little better, so its good as the normal solvent used in an extraction, while heptane or hexane by themselves would in this case be a bit more 'selective', so be better for the recrystallization. That being said, Ive used hexane/heptane for extractions, and it worked fine. Just have your mimosa well powdered, do at least 5 pulls, and the last two pulls make them for longer, over a whole day or more and with occasional thorough mixing, and warm them up, so that you get a decent yield. If you freeze precipitate, pre-evap till a quarter of the amount is left and freeze.