Ironically, I answer this question as someone who hasn't eaten meat in 25 years or so.  

 

As long as the blood has been drained, all parts of a kosher bird can be eaten.

 

As for what constitutes a kosher bird, the birds that are kosher are listed in the Torah and must be slaughtered in a kosher way.  Particularly in a liberal Jewish context, there is also the consideration of ethical kashrut, such as determining both how the animal is treated and how the workers are treated.

 

Poultry is considered meat in the context of kashrut, and traditionally cannot be eaten with dairy.

I think it depends on a number of factors.  

 

I'd have to ask a few questions, why is the seder a dairy seder? Is it because you prefer that food or because you (or some of your guests) are vegetarian? Also, do you normally keep kosher? Do you generally keep meat and milk separate? Do you keep a dairy home or do you generally have meat in the home?

 

There needs to be a balance between the tradition and your own, personal practice (not just in terms of ritual, but your general life practice).  If you are a vegetarian, especially one who is a vegetarian for ethical reasons, and the idea of purchasing meat is offensive, then I'd say that you should consider not using a shank bone.  Similarly if any of your guests fall into this category; if they will be bothered enough by the presence of the bone as to detract from their experience of the seder, then you might want to consider an alternative (or, if you do use a shank bone, to seat them on the other side of the table).

 

On the other hand, is the bone meaningful to you? Do you feel compelled to follow this tradition because it is a significant ritual in your observance of Pesach? If that's the case, you might want to include it.  Also, consider what about the tradition speaks to you if you want to consider an alternative (many vegetarian seders use a beet; I have seen people use a picture of a shank bone, also).

 

Remember, you're not eating the shank bone, so that could also make a difference.  Perhaps one solution could be to put the seder plate on some sort of a tray or placemat, so that there is a separation between the table on which you and your guests are eating and the one on which the ritual items sit.  Or even to put the seder plate on a small table or tv tray to the side, so that it's not even on the same table.  That way, the one meat dish is used as a meat dish, while the meal itself is dairy.

 

We are taught in Pirkei Avot 1:18 that, "The world stands on three things: On truth, on justice and on peace."  In order to maintain the balance of the universe, all three of these are necessary.  Ideally, these principles coexist in symbiosis with one another, but in reality, we know that is not always the case. So what do we do when, as in your question, two of these values are in conflict with each other--when the need to pursue justice is seemingly in conflict with the need to pursue peace? 

 

There is, of course, no easy answer.   And I believe that Israel's exchanging of prisoners in order to free the captive is, at its heart, about peace.  And as we learn many times in our tradition, there are many things that we can do--that we must do--in order to bring about peace.  I think that this falls into that category.  

 

Is it a perversion of justice? Perhaps.  But perhaps the ultimate justice for those who have done wrong is not for us to determine.  And in order to create a Middle East that exists with both peace and righteousness in equal measure, risks need to be taken and difficult choices need to me made.  If setting people free who have taken part in acts of terrorism, in order to save the life of one soldier, brings us one step closer to an Israel that can be full of peace, then I believe it's a risk worth taking.