p.282 core:
Mana spells: When using mana spells, the magician can only affect living things with auras or astrally active entities (such as spirits or foci) even in the physical world.
Active detection spells involve an Opposed
Test between the caster’s Spellcasting + Magic [Force] and either Willpower + Logic (+ Counterspelling if available) [Mental] for living things with auras, (Force x 2) for magical objects, or the object resistance for mundane objects (p. 295)
If the target is a living being, it must be a tissue sample. Tissue samples, however, decompose eventually and cease to become viable as a material link. (p.297)
Without attempting to read an aura, you can still get an impression of what type of aura it is (spell, ritual, spirit, living creature, foreboding horror from beyond all mortal ken, etc.). p.312f
Based on how the word "living being" is used and in general distinguished from spirits and magical objects, as well as being linked to cellular life (tissue sample), I'd say no, a Homunculus is not a living being as it's generally missing the qualifications for being a living being: Metabolism, growth, reproduction, homeostasis, organization and adaption.