I'm not sure what you mean. It seems to work fine:
openacs4=# create sequence sp_session_id_seq;
CREATE
openacs4=# create view sp_session_id_sequence as select nextval('sp_session_id_seq') as nextval;
CREATE
openacs4=# select sp_session_id_sequence.nextval;
nextval
---------
1
(1 row)
openacs4=# select sp_session_id_sequence.nextval;
nextval
---------
2
(1 row)
openacs4=#