De klimroute heeft een moeilijkheidsgraad en een moeilijke greep.

Because greep is a de-word, and in Dutch an adjective usually takes -e before a singular de-word, even after een.

So:

• de greep
• een moeilijke greep

Compare that with a singular het-word, where the adjective often has no -e after een:

• het boek
• een moeilijk boek

So the -e in moeilijke is a normal adjective ending.

Dutch very often forms compound nouns by writing them as a single word.
Moeilijkheidsgraad is made up of:

• moeilijkheid = difficulty
• graad = degree / grade

Together, moeilijkheidsgraad means degree of difficulty or difficulty rating.

This is very typical Dutch spelling. In English, we often write similar ideas as separate words, but Dutch usually joins them.

They are different kinds of words:

• moeilijkheidsgraad is a noun
• moeilijke is an adjective

In this sentence:

• een moeilijkheidsgraad = a difficulty rating
• een moeilijke greep = a difficult hold / grip

Even though both come from the idea of difficulty, they are used differently in grammar.

In a climbing context, greep usually means a hold, the place where you put your hand.

Outside climbing, greep can also mean:

• a grip
• a handle
• the act of grasping

So in this sentence, een moeilijke greep most likely means a difficult hold on the climbing route.

Because klimroute is a de-word.
In Dutch, every noun has grammatical gender/common class, so you have to learn whether a noun takes de or het.

Here it is:

• de klimroute

There is no simple rule that always lets you predict this from English, so this is mainly something to memorize with the noun.

Heeft is the third-person singular form of hebben = to have.

The subject is de klimroute, which is singular, so Dutch uses:

• de klimroute heeft

This works like English the climbing route has.

This is standard Dutch main-clause word order:

• De klimroute = subject
• heeft = finite verb
• the rest of the sentence follows

Dutch main clauses usually put the finite verb in the second position. This is often called the V2 rule.

So:

• De klimroute | heeft | een moeilijkheidsgraad en een moeilijke greep

That is completely normal Dutch word order.

Because the sentence mentions two separate singular nouns:

• een moeilijkheidsgraad
• een moeilijke greep

Dutch often repeats the article when two separate things are listed.
So this means the route has:

1. a difficulty rating
2. a difficult hold

You could not normally use one een for both here.

Not quite.

• moeilijkheid = difficulty
• moeilijkheidsgraad = degree/level of difficulty, often more like a rating or grade

So moeilijkheidsgraad is more specific. It suggests a measurable level, not just the general idea of difficulty.

Yes, it is grammatical and understandable. But depending on context, a Dutch speaker might choose slightly different wording.

For example:

• De klimroute heeft een hoge moeilijkheidsgraad.
  = The climbing route has a high difficulty rating.

• De route heeft een lastige greep.
  = The route has a tricky hold.

Your original sentence is fine, but in real climbing language, speakers might make it a little more specific or idiomatic depending on what exactly they want to say.