I would highly recommend not mixing or copying any .dll (.ma or any other binary) files from one product version (Bentley or otherwise) to another. Specific to this example MicroStation V8 XM edition was built using Microsoft Visual C runtime 7.1 and the current release of MicroStation V8i is built with Microsoft Visual C runtime 8.0. When Microsoft changes runtime versions they often change data structures and memory management operations that will potentially cause very high instability or immediate (unexplained?) crashes/exceptions. Please do not consider this option even if you do verify that old and new products use the same runtime - reason being that Products libraries theirselves undergo very similar changes where the function name remains the same, but the parameters, structures, or memory allocation techniques change causing previously mentioned instabilities.
Is there a reason that you cannot update your older version of MicroStation at home to keep things safe and simple?