Q:

When is it okay to use あります with a living subject?

When learning Japanese everyone's taught いる is for a living thing and ある is for non-living things. However, I recently saw the following sentence ...

あと、サッカー選手でもあります。

... which ends in ある / あります for a living subject, assuming were not talking about a dead soccer player!
Now the following make uses of ある sense to me:

〜である
  〜がある
  〜にある

But in my mind these adhere to the living/dead rule learned in those first Nihongo classes all those years ago. 
So where does もあります fit in? How should I think of this in English (equivalent phrase)?

A:

で（は）あります is the expanded form of です.  So when you say 「XはYです」, it is really 「XはYで（は）あります」.  From this, you can easily see the negative form (ではありません).  And also でもあります as in your example.  でもあります means "is also".

あの人はサラリーマンです。あと、サッカー選手でもあります。　→　That guy is a business worker (salary man).  He is also a soccer player.

That's the reasoning as to why it's あります in this situation.  As to why です is a contraction of で（は）あります and not で（は）います, I'm not sure.

A:

As istrasci and rintaun correctly point out, サッカー選手でもあります has a similar meaning to サッカー選手です. But it is true that ある is not the same word as です. What they don't explicitly point out and is crucial is that the ある used here is not a predicate. It is comparable to the English be. 

A is a soccer player
A is smart

In the sentences above, you can tell that the predicate is the noun/adjective phrase following be but is not be itself (in other words, be is not contributing to the meaning) from the fact that they can be used retaining their meaning, without be:

I consider A a soccer player
I consider A smart

On the other hand, be in the following examples is used to express existence, and is a predicate.

I think, therefore I am
There is a soccer player

The animacy restriction on Japanese ある and いる only concerns the predicate usage (the usage meaning existence or possession). While the following ある and いる are in the predicate usage,

A の書いた本がある
サッカー選手がいる

the following ある is not.

A はサッカー選手である
昨日のうちに買い物をしてある

Therefore, your example is a case where the animacy distinction is irrelevant.
Furthermore, as is well known, even the predicate ある can be used with animate subjects.

昔、ある所におじいさんとおばあさんがあった
A には子供がある

The distinction between ある and いる is actually much more complicated than mere animacy opposition.

A:

でもあります is actually derived from である (basically a written-Japanese way of saying です) and basically means "... is ... as well". For example:

AはBでもあります。 → A is B as well (in addition to something previously mentioned or understood).

Or the following:

彼は大学生であり、サッカー選手でもある。 → He is a university student, and he is also a soccer player.

