Yes, it is true and yes this material could be welded. It can be welding as per following standard.
ASTM 216/216M -"Specification for steel castings, carbon, Suitable for fusion welding for High temperature service"
Bad reputation of castings are due to,
1. Most of the casting standards are lenient in composition, heat treatment and inspection.
2. The control exercised by the foundries, due to lack of knowledge or economics, in both composition and heat treatments. Due to this the quality factor on general castings (derating factor) is specified in the ASME/VIII which with the proper NDE and testing could be again made 100%.
However since these additional NDE requirements are not mandatory (supplementary requirements) would be enforced only if specified in specific purchase orders. These (Radiography, LPI, MPI etc) ensures the structural rigidity.
It is possible for welding but definitely not recommended for strength concerns. Cast Iron/steel are brittle usually goes with high carbon content. Localized heat in the weld will result to residual stress on the spot and surrounding material, thus consequent to breaking and material fatigue when subject to external forces or pressure.