Not 100% sure what the question is, but sometimes you have no choice but to create System DSNs to help facilitate the connection.

The 32 vs. 64-bit driver issue could also play a role here, similar to what happens with SSIS. Designers as usually 32-bit applications and will use the 32-bit version of the driver. When scheduled, it could then be looking for a 64-bit driver unless specifically forced not to. I cannot confirm this however, as I have not tested this thoroughly with Oracle and SSAS Tabular recently.