Essentially yes, though he might have had to individually contact a few mathematicians to make his existence known. Consider the example of Ramanujan. Wpedia:
In 1912–1913, he sent samples of his theorems to three academics at the University of Cambridge. Only Hardy recognized the brilliance of his work, subsequently inviting Ramanujan to visit and work with him at Cambridge.
Do we know whether there are many Ramanujans who gave up before getting through to someone? One way to tell might be to look at such people who had already given up and were then discovered through a coincidence.
Recently, I gave some reasons for SIAI to begin publishing in mainstream journals, and outlined how it could be done.
I've recently been made aware of some pretty good reasons for SIAI to not publish in mainstream journals, so here they are: