The biological function of an intrinsically disordered protein (IDP) is based upon its conformational ensemble which is in turn governed by the IDP's amino acid sequence. In view of the different functions served by different IDPs, this ensemble-function view reinforces the physical expectation that the disordered chains of non-homopolymeric amino acid sequences---IDPs and unfolded chains of globular proteins---are heterogeneous, i.e., their ensemble distributions of conformations are different from those of homopolymers that habor a uniform intrachain interaction. Indeed, recent analyses indicate that conformational heterogeneity is key to reconciling the apparent inconsistency between IDP dimensions determined by SAXS and FRET. This development notwithstanding, it was stated recently that SAXS data on disordered proteins can be adequately accounted for by homopolymer chain models. It is important, therefore, to address the information content of SAXS data, to assess to what extent SAXS data can discriminate between heterogeneous and homogeneous conformational ensembles. We have conducted extensive simulations of subensembles of chain conformations with narrow ranges of radius of gyration Rg and end-to-end distance REE, and compared the molecular form factors (MFFs) and dimensionless Kratky plots of these highly heterogeneous (sub)ensembles with those computed for homogeneous ensembles. We find that the MFFs of heterogeneous and homogeneous ensembles are quite similar when the chain conformations are relatively open, suggesting that SAXS may not be capable of clearly distinguishing heterogeneous from homogeneous conformational ensembles of well-solvated or slightly compact chains. In contrast, MFFs for more compact ensembles are more sensitive to conformational heterogeneity. We have also developed an analytical theory for sequence-dependent MFFs. The theory provides insight into how different conformational ensembles that share the same average REE can have different average Rg's. Ramifications of our findings for the interpretation of experimental data are discussed.