I installed SP3 some time ago, and it killed RAID5 for me. Due to code changes in dmconfig.dll & dmadmin.exe (can see in WinMerge), you need to open the newest (sp3) files in a hex editor (I used FlexHex) and make changes to the new files. This time the offsets (where in the file you need to edit) are slightly different for two files, due to the new M$ code. I would not recommend using the older sp2 files after sp3 upgrades.
When I did this, I can boot fine, it recognized the array automatically (as healthy too - no rebuild needed), and I do not have to start it or anything.
dmboot.sys starting at offset 00011070h, the hex between brackets are the only bytes you need to change:
00011070h: 54007900 70006500 0000[5345 52564552
00011080h: 4E545749 4E4E5400 0000]0000 00004C41
dmadmin.exe starting at offset 00001C38h, the hex between brackets are the only bytes you need to change:
00001C38h: [77696E6E 74000000] 00000000 6C616E6D
dmconfig.dll starting at offset 00005140h, the hex between brackets are the only bytes you need to change:
00005140h: 4C414E4D 414E4E54 00000000 [57494E4E
00005154h: 54000000] 00000000 53455256 45524E54
Note the new offsets for all but dmconfig.dll. Don't forget to backup files you mod (before and after).
HTH
J