Can I use RMAN to backup and restore data in a certain point in time?
There is a feature specifically for that:  

 CREATE RESTORE POINT before_test1 GUARANTEE FLASHBACK DATABASE;
 select NAME,SCN,TIME from v$restore_point; 
 exec perform_my_test1;
 SHUTDOWN IMMEDIATE;
 STARTUP MOUNT;
 FLASHBACK DATABASE TO RESTORE POINT before_test1;
 DROP RESTORE POINT before_test1 ; 


This is a database's feature, not RMAN's (commands are for sqlplus), see doc for the full setup and disclaimers.  

To more precisely answer your question, RMAN can also be used for the task. The general script is:

run { 
  set until scn 123123123 ;
  restore database /* from tag ... */;
  recover database;
}


Don't use bare RESTORE DATABASE FROM TAG because without SET UNTIL it doesn't work as you'd expect in some scenarios.

I wouldn't say any of these two solutions are inherently safe, both have as many pitfalls as any other Oracle's advanced features, so you need to do some research upfront.