I want to be able to be able to ingest OBO formatted files into RDF4J in addition to Turtle, RDF/XML, etc...
It looks like OWL API has some parsers to do so but I am trying to avoid using OWL API. Are there other known ways of doing this?
All the OBO parsers I'm aware of use OWL API. You could take the source code for the obo module and replace all OWLAPI references with RDF4j - there are RDF4J adapters in the rio module to use for reference. But it is not a small undertaking.