yes delta mics are fine if you change the bolts,
but tbh, ive had delta mics on my car for a while and not changed the bolts.
but theres many types of spacers,
1, crappy little universal rings that go between the wheel,
2, long hubcentrics where your spacer fits the spigot on your hub, and has another spigot the same size on the end for the wheel to sit on,
these have 8 holes in them, 4 to bolt the spacer to the hub, then another 4 to bolt the wheel to the spacer, the 25mm spacers are defs this design, but im not sure on the smaller ones.
3, Smaller hubcentrics, these are like the crappy universal rings, but they too fit the bore of the hub correctly, and have a spigot on the spacer for the wheels to sit on, but like the first spacers, they only have 4 bolts and you just get longer bolts to fit. NOTE these are still refered to as hubcentrics as they still have to lip on the spacer.
if the spacers you buy are the 3rd, then getting new bolts will be really easy,
however if theyre the 2nd type, the bolts supplied (to bolt the spacer to the hub) have very short heads, and replacement bolts may be hard to find,
unfortunatley im not sure when they change from the 3rd type to the 2nd type, so may be best to know exactly what spacers your getting, but id steer well clear of the 1st type mentioned,
hope this helps.