These two articles are over 3 years old. Are they still relevant to ZP 1.4.4?

http://www.zenphoto.org/news/server-side-optimization

http://www.zenphoto.org/news/client-side-optimization

The mod to the .htaccess causes a server error, the gzip code seems to work fine.

Probably not. They are also clearly 3rd party and have never been tried by any of us.

The guys at Arvixe (they advertise hosting on your site) were recommending to me to use that code.

Just an FYI

Well, as said it is 3rd party so it may or may not still work. For sure htaccess file of Zenphoto changed naturally over the years so that part might need adjustment.
(I know that Arvixe advertises on our site but it is that, advertisement.)