Interline bagage and/or ticketing has nothing to do with an alliance. Bags can be checked through even if the two airlines are not a part of the same alliance.
If you are travelling on one ticket there IS absolutely no reason to think one might not be able to check bags through even when the two airlines are not a part of one alliance.
Airlines alliances is a relatively new phenomenon in the industry. Interlining has been going on gar longer than that.