This paper tackles the theoretical performance analysis of widely linear (WL) multiuser receivers for direct-sequence code-division multiple-access (DS-CDMA) systems, as well as their comparison with conventional linear (L) ones. In particular, receivers based on the minimum output-energy (MOE) criterion are considered, since they offer a good tradeoff between performance and complexity and, moreover, lend to some simplifications in the analysis. After comparing the ideal signal-to-interference-plus-noise-ratio (SINR) performances of the WL-MOE and L-MOE receivers, the paper establishes finite-sample performance results for two typical data-estimated implementations. Specifically, by adopting a first-order perturbative approach, the SINR degradation of the data-estimated WL-MOE receivers is accurately evaluated and compared with that of its linear counterpart. Simulation results are provided to validate and complement the theoretical analysis.