No, that mod site is not exactly "legal" as it has mods that use models and resources from other games.
Not to mention that Lovers Lab also looks to be the type of site that will get you viruses, Trojan horses, and rootkits if you download something. It doesn't look like a very secure website to me. TES Nexus is a far better site, as it has a large user base, and moderators who help to ensure that things like file infections and piracy don't happen, and when they do, they take action. Steam Workshop is pretty safe from nasty things, but I've been hearing that it isn't moderated as well when it comes down to things like mod piracy, however. I think TES Nexus and Steam Workshop are probably two of the best places to download mods. There's probably others that are good, safe and legal, but I can't think of what they are off the top of my head.