I've been building wheels for 30+ years and here's my advice. I actually encountered wheels like yours with frozen spokes on a bike I overhauled last month. On the rear wheel, there were 13 frozen spokes and I ended up replacing all spokes in the wheel - it was easier to rebuild completely than put in 13 new spokes and true. On the front wheel there were 6 frozen nipples, and with considerable patience I managed to get them all unfrozen and true the wheel. It took about a week. I'd put a drop of oil on the spoke/nipple junction, spin the wheel hard in the truing stand to push the oil into the nipple, and wait a day. Then I'd try turning the nipples again. One or two nipples per day would come unfrozen, and I kept repeating until all nipples turned freely. So I'd suggest you keep trying with oil on the nipples - in fact, oil every nipple because the rest will seize eventually too. Use oil once or twice a day for up to a week. If they are still frozen after a week, you'll have to cut out the frozen spokes. Do this carefully with the rimstrip on the rim, because spokes under tension become projectiles when cut. If you can simply replace a couple of spokes, then the rim is probably fine if it has no cracks or flat spots and trues up easily. If you for some reason decide to replace all or a large number of spokes, it may be easier to start with a new rim just because it will true up easier, though it's not necessary if the rim is in good shape.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72