Currently the metric used_pct_max for the tablespaces in the Zabbix Agent 2 Oracle plugin returns the allocated and not the used percentage of the tablespace. Please change the sql statement to something like this:

old: ROUND(DECODE(SUM(df.MAX_BYTES), 0, 0, (SUM(df.BYTES) / SUM(df.MAX_BYTES) * 100)), 2) AS USED_PCT_MAX,

new: ROUND(DECODE(SUM(df.MAX_BYTES), 0, 0, (SUM(df.BYTES)-SUM(f.FREE)) / SUM(df.MAX_BYTES)* 100), 2) AS USED_PCT_MAX,

With this change you will get the same values as in dba_tablespace_usage_metrics.