"Summit approach" sounds to me, and I suspect to most mountaineers, as if all the hard work is behind them, and they are on the last few (hundred) feet. Summit attack certainly seems to be used in conjunction with base camp pretty often. Here's one "attack":

Full text of "The Age Of Mountaineering"
... which bores through the rock of the Eiger, they came out on the preci- pice ...... however, were still thinking in terms of another summit attack, ...
www.archive.org/stream/ageofmountaineer002646mbp/ageofmount...

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Note added at 14 hrs (2008-09-24 07:53:30 GMT)
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BTW, the expressions are NOT the same; I offer you:
"Einstieg": (1) attack;
"durchsteigen": to conquer, and
"Einstieg (2) either "a climb into" the unknown, or "an attack on" the unknown.