The image quality of fluorescence molecular tomography (FMT) can be significantly improved with diffuse optical tomography (DOT) guidance, by incorporating the prior optical properties information recovered from DOT into its forward photon propagation model. Although present studies all assume that the absolute transmitted excitation light intensity can be measured for DOT, the hypothesis doesn't hold for most cases, because some extent of deviation in the calibrated excitation light amplification factor is inevitable in a non-laboratory (i.e., in vivo) imaging environment. In this paper, we evaluate the impact on FMT reconstruction accuracy of the use of hybrid DOT guidance and normalized born method. Results demonstrate that the quantification ability of FMT with DOT guidance alone varies greatly as the absolute deviation in excitation light amplification factor increases. In contrast, the hybrid method investigated is robust to the deviations, suggesting that the hybrid of DOT guidance and normalized born method is essential for quantitative FMT in complex in vivo conditions.