Is it okay to use gel and hair concealer after hair transplant?

You can use hair products and concealers after surgery based on what your doctor recommends. Every doctor is different in their post operative care instructions.  5 weeks may be enough in general but it is always a good idea to keep your doctor in the loop.

It is fine for you to use a concealer and gel at this point.  I instruct my patients that they can begin to use a concealer five days following transplant if they wish to cover any residual redness or blush color. With appropriate post-procedure care including careful hair-washing beginning the day after transplant, the transplanted area should look clean with minimal redness within the first one to two weeks. 

Personally, before any chemical compounds or Irritant material be applied to the recipient site I like to wait a full six weeks however if you wish to camouflage the recipient or donor site then synthetic hair fibers or topic is a viable alternative without  irritating the scalp at the recipient site. Of course I am much less concerned about covering of the donor sites than the recipient sites. Not to worry !

In general you can use any products after a week or so from the procedure but you should double check with your doctor just in case.

You should be completely healed by this time and can return to your normal routine at this point.  In general, you can start using products after three weeks.

you can use whatever makes you comfortable in terms of products, gels, shampoos or conditioners. Your transplant should be fully healed by this time (5 weeks or even 2 weeks) so that you can return to normal management of your hair and styling.