There were definitely as many PDP-11's (most running UNIX) as there were DEC 10s in the glory days of the Arpanet.   VAXes only rolled out toward the end of the NCP era.    

However, the last NCP host table shows this statistic for DEC machines on the NCP Arpanet

VAX (UNIX):  58
VAX (VMS):  19

PDP11 (UNIX):  59
PDP11 (RSX): 6
PDP11 (MOS):  11
PDP11 (MINITS); 10

PDP10 (TOPS-20):  40
PDP10 (TOPS-10): 7
PDP10 (TENEX):   22
PDP10 (ITS):  4
PDP10 (WAITS): 3

I had all but forgotten about Local Host / Distant Host / Very Distant Host 1822 protocols.    I remember that BRL had a PDP-11/40 running ANTS (ArpaNet Terminal Server out of University of Illinois).   It got replaced by an 11/34 running UNIX when the Arpanet went to long leaders New Years 1981.