Tactile switches to meet EMC standards and IP67
IP67 seal is not easy :)  Maybe a silicon keypad with the gasketing built into the part?  Then just have to design your enclosure to compress it.  Or epoxy it in place.  

They make stock ip67 tact switches that are rather large.  Most IP rated products are bigger than say the button on an X-box controller.  

Again the problem comes down to then sealing that button to your enclosure with o-rings or epoxy.  Depends what you're making.

If you really end up having an EMI problem and you used silicon switches you could probably put some flexible emi foam or gasket around it if you had to. That's starting to get fancy though, your all metal case with some small holes in might be fine.