Can temporal brow lift scars be placed on the hairline rather than within the hair?

There are different surgical techniques that can be used to lift the temporal brow. Not all of them require an incision in hair bearing skin.
Regarding your question, "can the incision be placed at the hairline". The simple answer is yes. The main concern is that these scars will be more noticeable than any hair loss you might get from incisions within the hair. It is also worth mentioning that trichophytic skin incisions can be used to preserve hair follicles at the site of future scars.

Dear dead metal
A temporal brow lift scar can be put at the hairline but as the skin in this area is very thin it can stretch as time goes by. Once things have healed you can cover it with make up as you mentioned yourself. Endoscopic brow lift scars are quite small and if you have surrounding hair to cover them , they could be hidden. There also the option of hair transplant onto the areas of scar if you develop alopecia. The surgeon usually orients his direction of skin incision so the hair follicles are not damaged but the risk of damage and subsequent alopecia always exist.

There are many incisions that can be used to achieve a brow lift. The simplest is placing the scar right on the eyebrow itself. Other incisions are hairline incision and scalp incision. The hairline incision can have great result with scars that are barely visible. It will also not raise your hairline. The scalp incisions are a good alternative because scars are hidden inside the hair. However, as you are aware, the scar can result in alopecia scar and the scar may be visible inside the scalp. This incision will also raise your hairline slightly. You should not be afraid of one type of incision. Different patients choose different techniques.

Correction of  brow sagging in the female. This can be done by a procedure I invented 44 years ago and have done hundreds for females and TG patients as well. The Irregular Trichophytic incision with a brow lift leaves no noticeable scar since hair will grow thru and in front of the incision! The excess bone is filed down and your brows can be raised to a more feminine and attractive appearance. See a very experienced surgeon who can show you closeups of his work.

You can do a lateral or temporal browlift by choosing a subcutaneous browlift.   This incision is made just inside the fine hairs of the scalp and elevates the middle and tail of the brow.

There are several ways to do a temporal brow lift.  One of these is to go right at the hairline - a pre-trichial brow lift.  You will get a small scar, but it usually heals well.  

The temporal brow lift is an excellent procedure. Though the incision is usually placed inside the hairline, placing it at the edge actually makes the procedure easier. If done properly, this scar also practically disappears. Just as a matter of information, I have not had any hair loss other than brief from scars within the hairline in over 30 years. It is a matter of attention to detail and how you make and then close the incision.