Just thought I'd say this here, if you're wanting to install mods that aren't visible via Steam Search, you can now do so in the Mods tab.
Note: Mods installed this way come with the disclaimer "if you know what you're doing you can add it anyway."
ARKServers.io will not be able to support mods installed this way, and as this solution bypasses a LOT of safeguards put into the back end cannot garauntee that installing such mods won't cause problems.
Also, since this also bypasses a lot of the pre-existing Steam Workshop hooks, you'll have to manually update manually installed mods. They will not auto update.
So to re-iterate, this is a feature for those that fit the bill of:
"if you know what you're doing you can add it anyway."