> Can you tell what should happen if i do a backup/restore?

If you able to backup and there are no logical errors in metadata
then you can restore and use it without problems

> I'm asking because i did a backup and it got up to the end without errors.
>
> [root@server1 tmp]# tail backup.log
> gbak:writing constraint INTEG_293
> gbak:writing constraint XPKV3$CONTATOS
> gbak:writing constraint R_943
> gbak:writing referential constraints
> gbak:writing check constraints
> gbak:writing SQL roles
> gbak:writing SQL role: PUBLICO
> gbak:writing SQL role: SOMENTELEITURA
> gbak:writing SQL role: PSINIT4_TOOL
> gbak:closing file, committing, and finishing. 1027317760 bytes written

Sounds much better that what gfix said ;)

> Also, my users are using this database all day and nobody noted
> anything strange.

Very strange. Are you sure error messages from firebird.log are from
the same database ? And generated at the same time you run gfix ?

> Is there some way to know which tables are pointerless?

You may lookup it by numbers (from firebird.log messages) in
RDB$RELATIONS

Regards,
Vlad