Tablespace on ephemeral storage
Oracle does not record checkpoint information in tempfile. So, for the tempfile:


Oracle is able to start even if tempfile is missing. You will get a message in the alter log and you should recreate tempfile.
No backup is taken of tempfile so it's safe to loose it
There is no need to trick with any storage parameter for tempfile if resides on ephemeral storage. 


About physical data structure are not tempfile, it is not safe to put them in the ephemeral storage. Oracle keep track of changes in the datafile even if you have disabled logging. Disabling logging will have only effect in the recoverability of the database, redo and overall performance. Does not permit you to put datafile on ephemeral storage. Opening the DB with a missing database (database does not take care of how important were data on it) will raise.

ORA-01116: error in opening database file %s
ORA-27041: unable to open file
ORA-01157: cannot identify/lock data file %s - see DBWR trace file
ORA-01119: error in creating database file '%s'


And you have to manually deal with the issue. Hence the use of ephemeral storage with normal datafile have to be avoided.