No, simply because GC isn't an optional part of ocaml's design. You can "disable" it only in the sense that you stop any frees from happening.
In order to do away with Garbage collection you'd need to completely change the type system, and while you might get a result which ends up looking a lot like ocaml, it won't be ocaml any more than ocaml is sml.
This is what Rust started out as, by the way. In my opinion, it should have stayed that way. Post-Mozilla Rust has been nothing but a gigantic disappointment.
Early versions of Rust "started out" with GC: the language was broadly similar to Golang, though with a lot of influence from Ocaml and functional languages more broadly. The comprehensive use of borrowck to avoid GC altogether was only implemented around 2014 or so, hence shortly before the Rust "1.0" release in 2015.
In order to do away with Garbage collection you'd need to completely change the type system, and while you might get a result which ends up looking a lot like ocaml, it won't be ocaml any more than ocaml is sml.
This is what Rust started out as, by the way. In my opinion, it should have stayed that way. Post-Mozilla Rust has been nothing but a gigantic disappointment.