When u put ur tablespace in hotback up mode,oracle will perform a checkpoint by writing all the modified blocks in the database buffer cache into the datafiles,advancing the SCN in the logfiles and datafile ,after this initial checkpoint,no further checkpoints will be written to datafiles.So the changes will be written to logfiles generating more redo till u end the backup.So i guess it really does not cause any issue if you dont switch logile.If at all u switch logfile before you take hotback up u will be writing into a fresh redolofile.

I hope i am write on this point.please correct me if i am wrong.

regards
anandkl