If you have laser-straight rows thanks to the GPS, and you have GPS on your cultivating tractor, it seems like you might be able to get by without camera guidance, provided you don’t have a lot of sloped ground that would shift your cultivator into the crop!
This seems to be the case - at the Aarhus University research farm (where the fields are very flat), we use GPS for planting and inter-row hoeing in cereal crops. When returning to the field to hoe, the operator must manually ‘nudge’ the logged path to align the hoe blades and crop rows correctly at the start of each pass. In this scenario, where we rely on GPS alone for hoeing cereals on flat fields, we’re able to accurately cultivate at 15 cm row spacings (~6") with 8 cm hoe shares (~3").
If you have planted with RTK GPS autosteer then yes it is perfectly possible to then use the autosteer to guide the hoe. I considered this to be the ‘killer app’ of interrow hoeing taking it from a specialised task using tool carriers or a driver on the hoe, to a standard 3 point linkage operation. I was using such systems in the mid 2000s in NZ on a wide range of crops and we were able to achieve crop gaps, i.e., the distance between the tip of the hoe blades next to the crop of around 5 cm, which matches the ± 2 cm accuracy of full RTK GPS autosteer. We very rarely had to adjust the lateral position of the hoe, certainly not at the start of each row. However with larger machinery (we were operating 100 kW tractors and 6.5 meter bout / implement width, it would take several runs up and back down the start of the row to get the tractor in the exact lateral position.
If tractor auto steer was a killer app for interrow hoeing, then implement steering (what I call double steer) is a double killer app. This is where BOTH the tractor is on full RTK GPS autosteer, AND the implement (drill, hoe etc) has its own separate GPS antenna to that of the tractor, which is also full RTK GPS, which then operates a hydraulic side shift between the tractor and the implement. This then takes the ± 2 cm accuracy of the tractor steering and makes it even more accurate (though still limited by the RTK correction signals and the speed of light). The other major advantage of this system is that the tractor does not need to be in exactly the right location, as, as long as it is with the distance that the side sift can move, then the drill or hoe can be accurately over the row, even while it is lifted on the three point linkage, thereby eliminating the need for the tedious up and backing at the start of each row.
Further full RTK GPS makes a very stable platform for computer vision systems, which are unaffected by the RTK correction issues, and can therefore achieve as small a crop gap, e.g., 3 cm as the machinery can achieve, e.g., flex in large hoes, sideways oscillations of drill coulters, seed bounce etc.
So, it is entirely possible to have GPS only drilling and hoeing, but, there are also advantages of having both options if you have the money available.