Appearance of が after a て form

Question

In the game Persona 3, a teacher says this while talking about a poet they like as opposed to one being mentioned in the textbook:

…葛西もいいけど、先生、 最近は窪田空穂にハマってるのよね。 歌人としてが有名だけど、 随筆もとってもいいのよ。

I don't think I had ever seen が attach to a て form prior to this; I can see that it's meant to say that 窪田 is famous as a poet, but I was wondering how が ended up being added here as として is more than capable of adverbially delivering that meaning:

歌人として有名だけど

As a poet (he) is famous but

My assumption is that its been added to force the specifying emphasis that が can usually put on nouns onto として (the thing that is famous is specifically him being a poet), but I have trouble conceptualizing how this makes sense without first nominalising として somehow (and if I'm not mistaken, wouldn't としては be more appropriate here anyway because we're contrasting his poetry with his essays?)

1. Is attaching が to a て form grammatically legal, if so, how does it make sense
2. If my analysis of adding emphasis was correct, how does the meaning differ between using として…, としてが…, and としては… in this case

Answer 1

You are correct that this が is essentially adding a kind of emphasis. Some adverbial expressions such as ～まで, ～から, ～て may be used with an exhaustive-listing-が, just as a contrastive-は can be used at similar places:

• 明日からが難しいところです。
  It's tomorrow that the hardest part begins.
• ナイフで切るのは簡単だけど、ハサミを使ってが難しい。
  It's easy to cut it with a knife, but what's difficult is doing so using scissors.

歌人としては有名だけど will be taken as a contrastive expression ("Though he is famous (at least) as a poet, ...").