Never heard of this concern before. A little paranoia here? How do you know that oil is getting to the #3 rod bearing (or pick a number from 1 to 4)? When everything is put together correctly, it all works. If the oil nozzle is installed at the front of the block and pointed the right way, and if the #1 main bearing is getting oil (again, how do you know?), the timing gears are getting oiled. You just have to trust that it is put together right, and there's no reason for it not to work. If it will help you sleep better, I suppose you could drop the oil pan and see if oil drips out of the front of the engine.
Return oil from the filter may contribute to the oiling of the timing gears, but it is not the primary source of lube oil for them, the nozzle in the front of the main oil gallery is. The source of oil to the filter is, however, very nearly the same place as the source of oil to the nozzle. If the nozzle is present, the passage to it is not blocked, and there is oil pressure present, the gears are getting oil. If the nozzle is not getting oil, the front main bearing and the cam bearing are probably not getting any either, and if that's the case, you will know it before long, or should maybe even know by now. BW