Ten spyte daarvan dat duiseligheid ontwikkel, val bloedskenkers nie flou nie.

It means despite the fact that or in spite of the fact that.

You can break it down like this:

• ten spyte van = despite / in spite of
• daarvan = of that
• dat = that

So Ten spyte daarvan dat duiseligheid ontwikkel literally works like:

In spite of that that dizziness develops

But in natural English, that becomes:

Despite the fact that dizziness develops

Because ten spyte van normally takes a noun phrase, not a full clause.

For example:

• Ten spyte van die reën = Despite the rain
• Ten spyte van die pyn = Despite the pain

But if you want to follow it with a whole clause, Afrikaans often uses:

• ten spyte daarvan dat ...

This is similar to English despite the fact that ...

So:

• Ten spyte van duiseligheid = Despite dizziness
• Ten spyte daarvan dat duiseligheid ontwikkel = Despite the fact that dizziness develops

Because dat introduces a subordinate clause, and in Afrikaans subordinate clauses usually send the finite verb to the end.

So:

• main clause order: subject + verb + ...
• subordinate clause with dat: subject + ... + verb

In this sentence:

• dat duiseligheid ontwikkel

Compare:

• Duiseligheid ontwikkel. = Dizziness develops.
• ... dat duiseligheid ontwikkel = ... that dizziness develops

That final verb position is very normal after dat.

Duiselig is the adjective meaning dizzy.

Duiseligheid is the noun meaning dizziness.

This is a common Afrikaans pattern:

• adjective: duiselig = dizzy
• noun: duiseligheid = dizziness

The ending -heid often turns an adjective into an abstract noun, much like English -ness in some cases.

Other examples:

• moontlik = possible
• moontlikheid = possibility

Bloedskenkers means blood donors.

It is a compound noun:

• bloed = blood
• skenker = donor
• bloedskenker = blood donor
• bloedskenkers = blood donors

Afrikaans, like Dutch and German, often forms compounds as one word. English sometimes writes similar ideas as two words, but Afrikaans commonly joins them.

So bloedskenkers as one word is exactly what you should expect.

Yes, literally val flou is something like fall faint, but idiomatically it means faint or pass out.

So:

• Hy val flou. = He faints.
• Sy het flou geval. = She fainted.

This is a fixed expression in Afrikaans. English does not normally say fall faint, but Afrikaans does.

This is the normal Afrikaans negative pattern: nie ... nie.

So:

• Bloedskenkers val flou. = Blood donors faint.
• Bloedskenkers val nie flou nie. = Blood donors do not faint.

The first nie usually comes after the finite verb or later in the clause, and the second nie closes the negative statement.

This double negative is standard Afrikaans grammar. It is not the same as non-standard English double negatives like I don't know nothing.

Because the sentence begins with another element:

• Ten spyte daarvan dat duiseligheid ontwikkel, ...

When a sentence starts with a fronted phrase or clause, Afrikaans usually keeps the verb in second position in the main clause. This is often called the V2 rule.

So the main clause becomes:

• val bloedskenkers nie flou nie

instead of the more basic order:

• bloedskenkers val nie flou nie

Compare:

• Bloedskenkers val nie flou nie.
• Ten spyte daarvan dat duiseligheid ontwikkel, val bloedskenkers nie flou nie.

That inversion after the opening clause is normal.

The comma separates the introductory subordinate clause from the main clause.

Structure:

• subordinate clause: Ten spyte daarvan dat duiseligheid ontwikkel
• main clause: val bloedskenkers nie flou nie

So the comma helps show the boundary between the two parts.

This is very common when a subordinate clause comes first.

Yes. A simpler version could be:

• Ten spyte van duiseligheid val bloedskenkers nie flou nie.

That means:

Despite dizziness, blood donors do not faint.

The original sentence is slightly more formal or explicit because it says despite the fact that dizziness develops rather than simply despite dizziness.

Here it is used intransitively.

• ontwikkel can mean develop
• in this sentence: duiseligheid ontwikkel = dizziness develops

So nothing is being developed by someone else; the condition itself develops.

Afrikaans also allows transitive uses in other contexts, depending on meaning.

It is historically an adjective meaning faint, weak, or dim, but in this sentence it functions as part of the fixed expression flou val / val flou = to faint.

So a learner should probably remember the whole phrase:

• flou val = to faint

rather than trying to translate flou word-for-word every time.

The core clause is:

• Bloedskenkers val nie flou nie.

That gives you a very useful base pattern:

• subject: bloedskenkers
• verb: val
• negative frame: nie ... nie
• complement: flou

Then the introductory clause is added in front:

• Ten spyte daarvan dat duiseligheid ontwikkel,
  • val bloedskenkers nie flou nie.

This is a good way to analyze longer Afrikaans sentences: find the simple main clause first, then add the extra material around it.