So I finally got my RZ57 spinning, and I am able to read and write
disklabels with the disklabel program. Currently I am using this one:

vuoep8# disklabel -rt sd0
rz57|Automatically generated label:\
        :dt=SCSI:se#512:ns#67:nt#15:sc#1005:nc#1928:\
        :pa#32160:oa#0:\
        :pb#64320:ob#32160:tb=swap:\
        :pc#1937640:oc#0:\
        :pd#1841160:od#96480:

First question:

I am not able to run newfs on what I intended to be the root
partition:

vuoep8# newfs /dev/rsd0a
newfs: /dev/rsd0a: Device not configured

But trying make a partition on the entire drive seems to work so far:
vuoep8# newfs /dev/rsd0c
/dev/rsd0c:     1937640 sectors in 1928 cylinders of 15 tracks, 67 sectors
        946.1MB in 121 cyl groups (16 c/g, 7.85MB/g, 1920 i/g)
super-block backups (for fsck -b #) at:
 32, 16192, 32352, 48512, 64672, 80832, 96992, 113152,
 129312, 145472, 161632, 177792, 193952, 210112, 226272, 242432,
 257312, 273472, 289632, 305792, 321952, 338112, 354272, 370432,
 386592, 402752, 418912, 435072, 451232, 467392, 483552, 499712,
 514592, 530752, 546912, 563072, 579232, 595392, 611552, 627712,
 643872, 660032, 676192, 692352, 708512, 724672, 740832, 756992,
 771872, 788032, 804192, 820352, 836512, 852672, 868832, 884992,
 901152, 917312, 933472, 949632, 965792, 981952, 998112, 1014272,
 1029152, 1045312, 1061472, 1077632, 1093792, 1109952, 1126112, 1142272,
 1158432, 1174592, 1190752, 1206912, 1223072, 1239232, 1255392, 1271552,
 1286432, 1302592, 1318752, 1334912, 1351072, 1367232, 1383392, 1399552,
 1415712, 1431872, 1448032, 1464192, 1480352, 1496512, 1512672, 1528832,
 1543712, 1559872, 1576032, 1592192, 1608352, 1624512, 1640672, 1656832,
 1672992, 1689152, 1705312, 1721472, 1737632, 1753792, 1769952, 1786112,
 1800992, 1817152, 1833312, 1849472, 1865632, 1881792, 1897952, 1914112,
 1930272,

vuoep8# mount /dev/sd0c /mnt
vuoep8# df /mnt
Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
/dev/sd0c      937826        1   890933     0%    /mnt


Second question:

I understand that it is not possible to boot directly off a SCSI
disk. But would it be possible boot with mop and then use the
bootparams to tell her to load the kernel, mount root and swap all
from the SCSI disk?

Ole