My question is if they add the column the table will be block during the coluum add because it's not enteprise but standard edition
Even in Enterprise edition, we will block (ie, wait for a quiet moment) but that should not cause significant issues, eg
Session 1
=========
SQL> create table t ( x int );
Table created.
SQL> insert into t values (1); -- no commit
1 row created.
Session 2
=========
SQL> alter table t add y number;
[blocked, waiting for session 1]
(New) Session 3
=============
SQL> insert into t values (2);
1 row created.
So the "alter table" will wait until all sessions handed their transaction, but will not block others.