Any Action that has been explicitly tested by the developer and rated for 7 will (or should) have that noted in the box under the version number (top right side of the page when you’re looking at the Action). Even if it isn’t listed there, it may work, or it may work with limitations.
You can help make this shared resource better yourself, by trying these “legacy” Actions in your new layout, and posting your findings in the comments on the Forge. Those get copied by mail to anyone who ever downloaded the Action, and the author. So it can be a nice way to let people in on what you find, and may spur the developer to make some updates.
It’s worth pointing out that 7 introduced a number of features around responsive design which may not work at all with Actions. (As in, cannot be made to work with Actions at all). This is because when an Action runs, it uses the layout as present in Freeway at the default setting, and does not get a second, third, nth pass at the page in the other breakpoints. I am hopeful that the wizards of Oxford have some ingenious way around this issue, but for now, only certain types of Actions (those that do not attempt to modify the geometry of an element, or react to that geometry at publish time) are going to be 100% perfect. That said, it’s not every Action that needs this sort of access to the page, and some can be rewritten to use JavaScript in the browser to measure the current size of things and adjust them as needed (that’s how the Carousel Action works). When this approach is taken, the usual test mechanism of “drag the browser corner around to see the breakpoints break” will not work as such – you’ll have to refresh the window at each size to see the new behavior.