Yes, crooked teeth can be indeed be ‘straightened’ with porcelain veneers or crowns. However, there might be a risk of nerve injury.
Let's examine the details. When you say crooked teeth, this means that your teeth are not aligned and we'd need to bring them into a well aligner arch. Teeth that are protruding will have to be trimmed sufficiently to make them go in line into the arch. Our teeth have a range of 1.5 - 3.5 mm of enamel and dentine thickness.
Imagine you have to bring the tooth in line by 2.5mm (which is normal when moving crooked teeth), you would have to trim away almost 3-3.5mm of tooth structure. Sometimes, this will encroach into the nerve of the tooth making root canal treatment necessary!
Personally, I would choose to straighten my teeth first, then place a thin veneers over it later. I would not trim so much of my teeth and place veneers just to straighten it and risking nerve injury.
If braces puts you off, you may consider one of the newest treatment method in teeth straightening, Clear Aligner Therapy. There are a couple of brands available now in Singapore.
That way, you don't have to content with metal braces that may be uncomfortable or unsuitable for working adults in the service line.
Hope this helps!