If the source CME is using SQL Server and the target SME is on Oracle, will I anticipate any issues migrating content from SQL server CME to Oracle CME via
Note that Content Porter is not intended for database migration purposes. It doesn't port all data in the system, you loose version histories and you will hit size limitations if you try to export your entire CM system.
If you only want to port a limited number of items (and don't care about the functional limitations), there should be no issues with different DB types for the source and target systems.
I would not expect any issue because the Content Porter calls the Tridion Core Service API which is an abstract layer on top of the database.
However I did not try it myself so will let others detail their experiences.
Is this for a migration or do you have disparate systems in your DTAP setup? I would not recommend the latter.
The problems you may spot are related to database and not to Tridion per se. Even more you might have problems migrating between the databases of the same type. For example: you may have different character set, this might result in some exotic characters being displayed differently or maximum name of an item be slightly shorter on one of the databases if use Chinese characters. But there should be no functional difference. If both databases are being setup according to Tridion installation manual, the only problem I foresee are slightly shorter item names on Oracle if use asian symbols