Yes you can most certainly wear retainers after a crown lengthening surgery, as long as the retainer does not impinge on the affected gums and area. Your orthodontist will be able to adjust your retainers easily for you.
On the other hand, it would be advisable to wait for at least 6-8 weeks after any gum surgery, before moving the teeth with braces. In general, we prefer to move the teeth first before performing gingivectomy or other such procedures, especially for the front teeth.
The levels of the gums may change after moving the teeth, so it would be best to place them in their final position prior to undergoing gingivectomy or crown lengthening surgery. If the surgery is for one of the posterior teeth such as the molars, then it is not so crucial as aesthetics will not be an issue.
Hope this helps!
Dr Geraldine Lee