Are adjectives ending with -ing considered non-finite verbs?

The frightening tiger has eaten the scared doe.

They are adjectives:

[1] They can be modified by "very", which can't modify verbs.

[2] They can occur as complement to complex-intransitive verbs like "become": "It became quite frightening" / "He became quite scared".

[3] They can occur as complement to complex-transitive verbs like "find": "I found it quite frightening"/ "I found the boy scared and shivering".

But not all participles can be used as adjectives. The present participles of the verbs "sleep", "approach" and "retreat", for example, cannot be used as adjectives:

[1] They can't be modified by "very": *"She was very sleeping"; *"The train was very approaching"; *"The army was very retreating."

[2] They can't occur as complement to complex-intransitive verbs like "become": *"She became/seemed sleeping"; *"The train became approaching"; *"The army became retreating"."

[3] They can't occur as complement to complex-transitive verbs: *"I found her quite sleeping". *"I found the train quite approaching"; *"I found the army quite retreating"

The range of expressions that can occur as pre-head modifier to a noun is very large and varied: we don't want to call them all adjectives. "Frightening" and "scared" have the properties of indisputable adjectives and hence must belong in that class, but the others don't have the distinctive properties of adjectives and hence are analysed as verb phrases in examples like "a sleeping child", "the approaching train", "the defeated army.

Does that clear things up?