Reliably backing up a live database

Hello,

I am relatively new to SQL databases in general, and very new to
postgresql, so please be gentle.

My question has to do with how to properly perform a dump on a live
database, that I've sort of inherited. We have some developers that are
assisting with making some modifications, but I want to make sure that
something they told me is true...

I was told by one of the developers (who admits that he is still
learning postgres) that I could get a successful dump of the live
database using the following command, and more importantly, that I could
do this safely without stopping the database first:

./pg_dump -U postgres  -Z --blobs --oids --encoding=UTF-8 dbname >
dbname.sql.gz

First, will that command result in a dump file that can be used to
perform a full restore in event of a catastrophe (these will be uploaded
to off-site storage)?

Second, can this command be run safely on a running database, or should
the database be stopped first? If the latter, would someone be so kind
as to provide an example of the commands necessary to stop this
database, perform the dump, then restart it, that I could put in a cron job?

Thanks in advance for any help...

Simon