I have installed VFD's on many older non-inverter motors and so far have not had any problems.
I have two mills in the shop which have the older pancake style 3ph motors circa 1980, they both run up to double their base speed of 1745.
Some of the things that classify a VFD rated motor are the wire insulation grade to withstand the high switching pulses, although I believe all motors built in the past 20yrs at least will have high grade enamel.
Balancing and bearings are the other two concerns.
I usually use a rule of thumb that 2 pole I never run above the base speed of 3600 and 4 pole I usually run double base speed up to 3600.
I usually figure than most motor manufacturers who build 2p & 4p motors are pretty much going to be of the same design as each other, apart from the pole issue of course.
The above applies to non-inverter motors, Inverter grade motors usually have a max speed as well as base speed on the label.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.