Yes that is true. The R-37, for example, does not require a missile rail with its default setting. So one should open the missile data ini with weapon editor and check the respective check box. Then, once the missile is selected, the game will know that it should load the missile with a missile rail (if there is actually one as part of the model of that pylon)
[WeaponData001]
TypeName=R-37
FullName=R-37 Arrow
ModelName=R-37
Mass=600.000000
Diameter=0.380000
Length=4.200000
SubsonicDragCoeff=0.632000
SupersonicDragCoeff=0.866000
AttachmentType=SOVIET
SpecificStationCode=
NationName=Soviet
StartYear=1997
EndYear=2020
Availability=1
BaseQuantity=80
Exported=FALSE
ExportStartYear=0
ExportEndYear=0
ExportAvailability=0
WeaponDataType=1
RailLaunched=FALSE <-- should be TRUE here for the game to load the missile on a pylon with missile rail
RocketPod=FALSE
Retarded=FALSE
FinStabilized=TRUE
SpinStabilized=FALSE
HasGrowl=FALSE
EffectClassName=LargeMissileEffects
ReleaseDelay=1.000000
WarheadType=0
Explosives=60.000000
FusingDistance=2.000000
ClusterBomblets=0
ClusterDispersion=0.000000
GuidanceType=13
Accuracy=95
MaxTurnRate=24.000000
MaxLaunchG=7.000000
LockonChance=90
LaunchReliability=90
ArmingTime=2.000000
SeekerFOV=6.000000
SeekerGimbleLimit=40.000000
SeekerTrackRate=16.000000
SeekerRange=250000.000000
CLmax=16.120001
MinFreq=0.000000
MaxFreq=0.000000
MinLaunchRange=3700.000000
MaxLaunchRange=250000.000000
Duration=300.000000
CounterCountermeasure=90.000000
NoiseRejection=90.000000
CapabilityFlags=0x1000002f
LoftAngle=0.000000
DescentAngle=25.000000
MaxLoftAltitude=0.000000
BoosterStart=0.500000
BoosterDuration=10.000000
BoosterAccel=32.000000
BoosterEffectName=MissileFireEffect
BoosterSoundName=Missile
BoosterNodeName=
BoosterPosition=0.000000,-2.000000,0.000000
SustainerDuration=240.000000
SustainerAccel=25.000000
SustainerEffectName=MissileFireEffect
SustainerSoundName=Missile
SustainerPosition=0.000000,-2.000000,0.000000
InFlightEffectName=MissileInFlightEffect
InFlightSoundName=
ReleaseAnimationID=-1
EODisplayFlags=0
CEP=0.000000