I think that one of the reasons that UTHs work so much better than heat lamps is that they do not dry out the air as much. This allows for better regulation of humidity for your BP.
Also, in the wild, the snakes depend on the suns heat to heat rocks or the ground, which in turn radiate heat from below (belly heat)
By putting a piece of slate or something similar under a heat lamp a similar effect of an UTH could be created, but heating all of the above air would still lower the humidity.
0.1 Corn Snake (Anery), 1.1 JCP (High Yellow), 1.1 BRB, 1.0 Albino BCI, 0.1 Het Albino BCI, 1.0 GTP (Jayapura type)