Yes one tablespace can hold objects from different schemas.Eg. when we create any schema (user) than we can assign default tablespace like this for any user user we can use same tablespace.

Eg. SYSTEM tablespace in oracle database, which is used by all default users whos default tablespace are not mentioned. or

all user will user system tablepsace as default tablespace if their default tablespace is not mentioned at the time of user creation.