The character formula should be viewed here as a purely formal statement about weight multiplicities in the irreducible representation, so the analytic-looking exponential notation for compact Lie groups doesn't really add anything significant to the combinatorics.   (The roots and weights actually live in the dual of the Cartan, but Killing form duality allows your identification.)   The "sum equals product" formula is at the heart of the Weyl formula, but isn't simple to prove in the original compact Lie group setting.   It gets much easier to see in the algebraic setting pioneered by Bernstein-Gelfand-Gelfand, which recovers the Weyl formula as related to Kostant's later weight multiplicity formula (the two eventually being in fact equivalent).   This is all done in the setting of Verma modules in their early 1970s papers, within the BGG category $\mathcal{O}$.     

Anyway, it's important to be flexible about translating the compact Lie group formula as Weyl proved it into the setting of complex semisimple Lie algebras.  This allows also for a beautiful generalization of the Weyl denominator formula to the infinite dimensional setting of Kac-Moody algebras.   There you see connections with much older infinite "sum = product" identities going back to people like Jacobi and Euler.

Is there some geometry hidden here?   Maybe yes, but that's a longer story.