Yes, if it is improperly set up. This article states that the FBI was able to access an onion website via direct IP address. From the article...
Due to a misconfiguration of the server hosting the TARGET WEBSITE
[Playpen], the TARGET WEBSITE was available for access on the regular
Internet to users who knew the true IP address of the server
“Basically, Playpen must have set their [child pornography] site to
[a] default [web server setting], meaning if you typed in the IP
address you could see the Playpen site,” Thomas White, a UK-based
activist and technologist, explained in an encrypted chat. “Whereas if
they set another default like ‘server not found,’ then you could only
access Playpen by typing the correct .onion address.” This means that
law enforcement could verify that an IP address belonged to a specific
An FBI Agent, acting in an undercover capacity, accessed IP address
188.8.131.52 on the regular Internet and resolved to TARGET WEBSITE,” the document continues. That address pointed to a server in
North Carolina, hosted by a company called CentriLogic.
The FBI was tipped off about Playpen’s IP address by a foreign law
enforcement agency, as noted in other, redacted versions of the
warrant. This recently unsealed version includes detail on how that IP
address was left exposed.
It is not clear how the foreign law enforcement agency discovered
Playpen's real IP address in the first place. But the main
administrator of the site, who the FBI suspects is Steven Chase from
Florida, was clearly aware of the problem and actively trying to fix
it, according to the search warrant application.