Apart from tonic, is there other way in which we can use grpc by compiling protos?
Sure, quite a few. AFAIK tonic itself doesn't do any serialization of protobuffers but relies on prost to do that.
In my use case, I want to manually compile the protos rather than using rust crate for building it.Is it possible for me to use protoc compiler to compile protos?
There are:
that allow you to generate Rust code from .proto files.
There is also a protoc plugin called protoc-gen-rust you could use if you don't want to write your own program around the crates I linked above.