No all transaction levels are implemented on the lockTablesForSchemaSnapshot function, file SqlServerSourceInfoStructMaker.java.

Doc:
[https://docs.oracle.com/javase/8/docs/api/java/sql/Connection.html#setTransactionIsolation-int-

void setTransactionIsolation(int level)
throws SQLException

Attempts to change the transaction isolation level for this Connection object to the one given. The constants defined in the interface Connection are the possible transaction isolation levels.

Note: If this method is called during a transaction, the result is implementation-defined.

Parameters: Level - one of the following Connection constants:

• Connection.TRANSACTION_READ_UNCOMMITTED,
• Connection.TRANSACTION_READ_COMMITTED,
• Connection.TRANSACTION_REPEATABLE_READ, or
• Connection.TRANSACTION_SERIALIZABLE.

(Note that Connection.TRANSACTION_NONE cannot be used because it specifies that transactions are not supported.)