Yes; subscribing your #snac to a relay has two benefits: 1) you reach a big stream of posts where you can "fish" those with the hashtags you like, and 2) your posts are also sent to that stream, so that other relay subscribers can receive them. FediBuzz doesn't provide 2.

On the other hand, the FediBuzz concept has the benefit that you only receive those posts you are interested in and not a firehose of data (most of it probably of no interest for you), which is a huge benefit if you have bandwidth restrictions.