It all depends on the quality level you expect of the repair. Yes you could use filler on that hole, but to do it properly you would use a dremel or nibbler to excise all the rust. Just cut it away. Sand or grind to shiny metal around the edges. Then you would weld in
some metal with a mig. Prime the backside with POR or cold galvinize.
Look for a filler called "ALL METAL". I would use this filler even if you are not going to weld. Mix the filler and apply, shape with a "cheese grater" file and sand to shape, repeat as needed. Spray with high build 2 part primer, block sand, spray again, squirt a guide coat of flat black, block,
and finish sand with #400. Spray your topcoat. If you aren't going to weld, then do the same steps but use a fibreglass mat to back the hole.
Mix up your filler and saturate the mat with it. Press the mat from the back of the hole. Let it set up, then do your build up with filler in the same way, as if you welded. The fibreglass mat becomes your "metal" patch. If you are careful to remove all the rust, this type of patch has lasted a good long time for me, although since I am able, I always weld.

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