Teresa May has cast in her lot with some fringey protestant group (needed for a coalition... or did that ever happen?)
Yup, they don't have a formal coalition, but a slightly more detailed version of a confidence and supply agreement. The interesting thing is that they've both agreed to stick to the Good Friday Agreement, which pretty much rules out a hard Irish border as it was agreed at a time when the EU had abolished internal customs borders, and the thought of Customs controls returning to the Irish border was unthinkable.
The Conservative-DUP agreement is why Northern Ireland will now be in the ridiculous position of being the only place on "those islands" where abortion will be illegal. The Tories wanted to change it, but there's a school of thought that suggests that only the Northern Irish assembly has the power to do so. Any attempt by the Tories to change it would probably result in the DUP tearing up the agreement, and they need those 10 votes to get legislation through.
Essentially, this is why there's no real answer to the Irish border question. If customs barriers go up on the NI side, they'll be attacked and destroyed. The UK can do as they did during The Troubles and simply not bother to control goods, but that's hardly viable in the era of goods freely moving around once they're in the EU. Dublin will also bring a case against UK for breaking the Good Friday Agreement if customs barriers go up, and this could cause things to get worse again, especially in places like South Armagh where they're always ready for a fight.
The most sensible solution would be for NI to remain within the EU Customs Union, but the DUP want close integration with the rest of the UK and won't support a Customs line down the middle of the Irish Sea. If they propose such a thing, the DUP will break the Agreement and May's government will probably fall as a result.