Any clear wood finishing product such as an oil or varnish will darken the wood slightly. To get an idea of how this will likely look, you can wipe the bare wood with a clean cloth dampened with water. Water, the clearest of liquids will darken the porous surface of the wood despite being totally colourless. It would be fair to say that wood oils will change the wood more than a varnish as it penetrates the woods surface. Water-based varnishes tend to change the colour of the wood the least.
In terms of rectifying the situation you could try dampening a clean, uncoloured, lint-free cloth or rag with White Spirit and wiping over the door. The white spirit will break down the Polyx Oil and should remove much of it from the wood. Take care not to soak the door with white spirit as this may cause issues with the glue that holds the veneer in place. Sanding may also be a solution but without knowing how thick the veneer is, its probably better to hand sand rather than use a power sander. A combination of white spirit and then light sanding may be required. When sanding, use a 120 Grit abrasive and no finer. Finer sand paper can cause absorption issues when re-oiling the doors. When doing any of the above, do a small test area on one of the doors to assess effectiveness and final results. It might be worth checking with the door manufacturer first to find out what they say about using white-spirit or sanding the doors. They may advise against one, the other or both methods.
To avoid this darkening effect, there are some oils specially developed to retain the natural, untreated look of the wood such as
Fiddes Hard Wax Oil Natural
and
Osmo Door Oil Raw 3033
. These products contain a small amount of white pigment that counteracts the darkening associated with clear products. The amount of white is minimal and if applied correctly, will not appear white on the wood. These products are only suitable for lighter coloured timbers such as Oak, Pine, Fire and Spruce as examples. If applied to dark exotic hard woods they may give a slightly milky appearance.