That can be answered with both "yes" and "no".

Almost all digital images go through some form of post-capture processing, whether that be during the "development" of RAW images on a computer or merely the conversion to JPEG using a picture style in the camera. These sorts of adjustments are very much analogous to what we would do in the old days when selecting a film to use, choosing the processing method, and perhaps making and developing the print. For these sorts of adjustments, Photoshop (or one of its immediate competitors) is an awkward, but thoroughly legitimate choice. (Something like Lightroom is a much easier environment to work in for these more global adjustments than, say, the Adobe Camera Raw window in Photoshop.)

After that, it really boils down to intent. In this case, you are trying to make up for the deficiencies of your camera. A purist approach would be to either accept the image as your camera provides it or, if your camera can't provide the image you intended, change your camera. And that purist approach is all well and good as far as it goes, but it's expensive and prevents you from taking the pictures you want until you've paid the entry fee to join the club. As you progress down the rabbit hole that is the photographic hobby, you'll probably begin to acquire gear that is more suitable to whatever style you develop. But if you can express your vision in the meantime only through manipulation, then that is certainly legitimate.

On the other hand, using something like Photoshop to make up for deficiencies in your photography on a regular basis would be a bad habit to get into. Sure, we've all blown the shot at some point and had to rescue it through heroic action, but that should be a fairly rare event. If you find that you're being careless with the camera because you can "fix it in post", then you've gotten into a bad habit. If most of your images need to be recomposed or need major exposure adjustments, then you're relying too much on the software, and should probably try to go Photoshop-free for a period (even if that means shooting camera JPEGs exclusively) just to break you out of that habit.

The object of the game here, no matter what the end product may be, is to get things as right as you can in camera before you proceed to manipulation. That applies to "straight" landscapes and photojournalism, but it also applies to complex composited creations that could never have been shot "straight".

On to the specific topic of bokeh in post: you'll probably find that a plugin such as Topaz Labs Lens Effects or Alien Skin Bokeh 2 will do a much better job than you can do with the native tools in Photoshop (or similar), since they'll allow you to create a depth map or depth gradient to realistically simulate shallow depth of field effects.