You might be able to get away with it. It's in a worse location on the smallest cog, compared to if it were on the largest cog, because the small cog doesn't have many teeth to begin with.

As rjacob pointed out, it looks as if the cog is cracked, perhaps from impact. I don't think that it will self-destruct, but it probably won't shift well, the chain may hop, and it has the possibility of hurting your chain.

I'd try it - if it works well enough, ride it but watch it to see if the crack worsens.

On the other hand, you can get a new 6-speed freewheel for $20.