Yes but with a few caveats.
1) The 16Mb drive is quite a bit quicker than the 8Mb ones so will spend a bit of time waiting for the other drives to catch up. Far from a major worry though, it won't prevent you from doing what you want to do.
1b) I assume we're talking about three drives the same size here? If not you'll lose some space on the new one.
2) If you're RAID controller doesn't support Capacity Expansion you'll need to nuke the existing array and start from scratch. Most modern controllers do support expansion though.
3) If you can expand the array the controller won't touch the contents so you'll end up with the same size of partition(s) as you have just now and some empty space. You'll need to use diskpart, Partition Magic or something similar to expand your existing partitions. Alternatively you could just create a new partition in the new space.