DMT wont dissapear/break down with a bit of heat, so in terms of weight, total yield should be the same either way. The only thing that can happen is if you use heat to speed up evap, it might interfere with crystallization and part of your product be oily and not crystallize well.. This could theoretically be some dmt n-oxide forming, which is still psychoactive but it is an oil, so you could have a mixture of n-oxide and dmt.
Another possibility why the oil might happen is just trapped solvent together with your product that prevents dmt from properly crystallizing (I think this is what usually happens). In my experience if you insist on scraping/rescrapping and letting dry, it will eventually dry to a waxier consistency. Also you can always recrystallize to make it into nicer crystals again, just redissolve in minimal amount of warm naphtha and freeze.
Why dont you freeze precipitate though? If you just use a little heat/fan to pre-evap and then freeze, you should be fine and will still get crystals.