No, there is nothing wrong with paying an artist, but just remember that there are three ways to do this:
Back-End
Front-End
Mixed
Back-End means that the artist is on the same footing as the writer. Usually, a pair of starving creators trying to take a gamble and make something of it. Both are doing it for a variety of reasons, most of which are far to familiar to the people reading here to list them again.
This means that the IP should be split, just like the profits and the workload are being split. That's something that a lot of writers don't think about, is the split of the IP, but it all needs to be taken into account, and the workload divided before the partnership kicks off.
Front-End means that the artist is being paid up front (usually by the publisher, though some seem to think the writer should do it) on a work-for-hire basis, owns nothing on the IP, and in some cases does not even own the finished artwork, or if they own the physical art, do not own reproduction/publication rights to it.
And Mixed, which is a very uncommon mix of some money up front, and some more off the back end.
None of the models are perfect, and all of them have extreme problems.
But if you have the capital, and can afford to pay an artist Front-End, go ahead. You will own the artwork, don't have to split the profits if you hit it big, and can have them redo anything that is not up to your agreed upon specs. They are a freelancer working for hire, and what you will get depends on the honour and integrity of the artist, and how much money you are tossing at them.
Do not pay until the work has been delivered. You can pay on a per page basis, but do not give them a deposit, make sure you have a contract, and make sure it does not strip you of any of your IP rights. It is usually customary to return the original art to them, as you are not buying the art, but the rights to it. Make sure that you have unlimited reprint rights, as well as the rights to use it for other purposes such as advertising and merchandising. If it is digital, make sure what you are getting is print quality (300 DPI or better).
Oh, and pay on the agreed upon schedule, promptly upon receipt of your art.
Eagle
(I've had bad experiences on both sides of the work-for-hire art biz)