Add this to your .Xdefaults file and start your VAX session with
'aixterm -v -name vt100 -e telnet MYVAXHOST'

-----
vt100.vt102: true
vt100.fullcursor: false
vt100.translations:    <Key>F1: string(0x1b) string("OP") \n\
                       <Key>F2: string(0x1b) string("OQ") \n\
                       <Key>F3: string(0x1b) string("OR") \n\
                       <Key>F4: string(0x1b) string("OS") \n\
                       <Key>KP_0: string(0x1b) string("Op") \n\
                       <Key>KP_1: string(0x1b) string("Oq") \n\
                       <Key>KP_2: string(0x1b) string("Or") \n\
                       <Key>KP_3: string(0x1b) string("Os") \n\
                       <Key>KP_4: string(0x1b) string("Ot") \n\
                       <Key>KP_5: string(0x1b) string("Ou") \n\
                       <Key>KP_6: string(0x1b) string("Ov") \n\
                       <Key>KP_7: string(0x1b) string("Ow") \n\
                       <Key>KP_8: string(0x1b) string("Ox") \n\
                       <Key>KP_9: string(0x1b) string("Oy") \n\
                       <Key>KP_Divide: string(0x1b) string("OQ") \n\
                       <Key>KP_Multiply: string(0x1b) string("OR") \n\
                       <Key>KP_Subtract: string(0x1b) string("OS") \n\
                       <Key>KP_Add: string(0x1b) string("Om") \n\
                       <Key>KP_Enter: string(0x1b) string("OM") \n\
                       <Key>KP_Decimal: string(0x1b) string("On") \n\
                       <Key>Next: string(0x1b) string("Ol") \n\
                       <Key>Left: string(0x1b) string("OD") \n\
                       <Key>Up: string(0x1b) string("OA") \n\
                       <Key>Right: string(0x1b) string("OC") \n\
                       <Key>BackSpace : string(0x7f) \n\
                       <Key>Down: string(0x1b) string("OB")

You should also add

XENVIRONMENT=$HOME/.Xdefaults
export XENVIRONMENT

to your .profile.

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