It should work if you use valueDate="SYSDATE" instead of value="SYSDATE".
Liquibase doesn't inspect the table to determine the type, so
value="" normally assumes it's a string and needs to be
quoted but there is a special case for the "current time"
function which is set to SYSTIMESTAMP for oracle.
Using valueDate instead tells liquibase the value is a date and if
it's a known date function to not quote it which should resolve
your issue.
Nathan