We compare resonant electronic Raman scattering and photoluminescence measurements for the characterization of a spin-polarized two-dimensional electron gas embedded in Cd(1-x)Mn(x)Te single quantum wells. From Raman scattering by single-particle excitations in a zero magnetic field, we measure the Fermi velocity and then obtain the Fermi energy (as well as the electron density), which is comparable to that extracted from photoluminescence for moderate electron densities, assuming a bare band-edge mass. At large electron densities, the Fermi energies derived from Raman scattering and photoluminescence differ. For an applied in-plane magnetic field and zero wave vector transferred to the electron gas, Raman scattering spectra show peaks at both the Zeeman energy Z, resulting from collective excitations of the spin-polarized electron gas, and the one electron spin-flip energy Z(*). Magnetophotoluminescence spectra show conduction band splitting that are equivalent to Z, suggesting that collective effects are present in the photoluminescence spectra. Assuming an uncorrected band-edge mass, the degree of spin polarization zeta determined from the magnetophotoluminescence line shape is found to differ from that derived from the magnetic field dependent Raman scattering measurements for large electron densities. We attribute the discrepancy in measuring zeta and the Fermi energy to the renormalized mass resulting from many-body electron-electron interactions.