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Ok heres my take on both.
Seeing should actually be measure on a 1-10 scale. Seeing is most commonly vital for planetary work and close doubles. When seeing is at 1/10 little if any detail can be seen of any planet. In fact the image will dance around like it is in a washing machine. Little if any detail can be seen at all. When seeing is very good say from 7-10/10 the image of the planet will not move, it will be steady and lots of detail can be seen. This is even when transparency is around 5.
As to transparency this relates more to observations made of DSO's. Typically high cloud and dust particles will affect transparency. Fine detail of nebula and galaxies will be lost due to poor tranparency. Scale again is 1-10. You can still have good seeing even when transparency is very low. Light pollution will also be affected by transparency. In fact they are inter-related. If the sky has lots of dust particles in it, and you live in a city then the light pollution have a greater effect. The light bounces off all the crystals of dust or cloud and increases the light pollution. The best time for good transparency is usually after a big rain period. The sky will be crystal clear because the atmosphere has had a wash. This does not mean that seeing will be best either, that is because upper atmosphere winds can and do effect seeing.
A good example of what I mean is this. I live on the sound side of Adelaide. Most nights the light from the city will effect any viewing to the north. Being a city there is a lot of dust in the air, when the dust is really bad or there is high sirius cloud the transparency will be lousy typically around 4/10 and this will extend overhead and to the south. However even on nights like this I can sometimes get great seeing for planetary imaging. This is because the jet stream is calm overhead and local conditions are very clam. In addition even on nights when the sky is crytal clear the jet stream can make the sky twinkle and planetary work impossible.
So seeing is related to the air currents and transparency is related to things like dust, cloud and pollution. The two are not related to each other and are caused by different influences.
Hope that makes sense.
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