一、摘自 Practical English Usage，这本书是我唯一看到有特别说明名词只能接though（不能接as），且例句不带冠词（a/an）

255 as and though: special word order

adjective/adverb/noun + as + clause

As and though can be used in a special structure after an adjective, adverb or

noun. In this case they both mean 'although', and suggest an emphatic

contrast. (In AmE only as is normally used like this; though is unusual.)

Cold as/though it was, we went out. (= Although it was very cold,

... )

Bravely as/though they fought, they had no chance of winning.

Much as/though I respect your point of view, I can't agree.

Strange as/though it may seem, I don't like watching cricket.

After a noun, though can be used in this way (but not as).

Scot though she was, she supported the English team.

二、截图来自 A Comprehensive Grammar of the English Language，虽然没有特别说明，但也符合这个规律：名词只接though，不带冠词

三、朗文词典as词条，也没有接名词

Successful a man as he is (=As he is a successful man), he is not proud. 他虽然是个成功人士，但并不骄傲。 

Brave a man though he is (=Though he is a brave man), he trembles at the sight of snakes. 他尽管勇敢，可见到蛇还是发抖。

as/though引导让步状语从句，从句某个成分前置（不是倒装）是为了强调。当前置的是一个单数名词时，通常不用冠词。但像successful man, brave man这样的名词词组前置时，强调的其实不是名词，而是作定语的形容词，定语形容词被程度副词强调，是需要不定冠词的。所以，以上二句中，前置的定语形容词前省略了程度副词as. 所以，该句应该等于：

As successful a man as he is, he is not proud. 他虽然是个成功人士，但并不骄傲。 

As brave a man though he is, he trembles at the sight of snakes. 他尽管勇敢，可见到蛇还是发抖。

以下为COCA的二个理解：

As wise a man as he is, Fed Chairman Alan Greenspan has not been wise enough to realize the problems he caused by ending the dollar inflation, ...

As mild a man as he seemed, he had lived steadily in the service of his passion; ...

@yesmina: 请问一下,我也查了一下English Practical Usage, 查到了您的例句,但没有查到那条用法说明。请问您用的是哪个版本？

   as 引导让步状语从句时，如果从句里的表语是可数名词单数形式，该名词前面不能用不定冠词，即使名词前面有形容词，也习惯不用不定冠词。例如：

    Great scholar as he is, he is lacking in common sense. 他虽然是个大学者，但是他缺乏常识。（摘自王福祯、王芳、许鸿主编《英语词语用法详解词典》p.90）