You can absolutely do anything you can do in Erlang in another language. Some tasks will be easier, or harder, however.
In my mind, Erlang excels in a few ways:
Less often remarked, binary parsing in Erlang is rather nice. Parsing out an IPv4 packet looks like this:
> = Payload,
OptsSize = (IHL - 5) * 4,
> = IPRest,
And then you've got everything. As long as formats are reasonably documented, it's easy to parse them. Sometimes, you can even parse a size and use the size in the same match.
More often remarked; because of the language constraints, most notably a lack of shared memory between processes and immutable variables, most programming ideas end up expressed in a way that's amenable to massive concurrency, while being comprehensible. Most Actors have easy to understand behavior --- they may accept messages, leading to them sending messages and changing their internal state. From there, you may need to puzzle out the overall system behavior, but often times, getting each individual Actor's behavior correct, leads to correct (if hard to verify) system behavior.
Hot loading code reduces deployment time, which increases developer productivity. When you've got a million users connected to a machine, it takes a lot of time to move them to other machines so you can do a traditional stop / start cycle; hot loading means you can fix things in seconds (and, of course, it means you can break things in seconds too). You can, of course, hotload in C, and probably other languages, but very few people do it. It's comparable to pushing PHP files though.
And, of course, the most important thing is ejabberd is in Erlang, and it looks like it has what we need for a chat server, and I heard some other people scaled it really far. ;)