The subject of Spiegel article is the AK47 designed in 1947 and, as that article suggests, now considered somewhat obsolete and inaccurate.
Calibre: 7.62 vs 5.56
The AK47 uses a 7.62×39mm round.
Under US influence, NATO switched from 7.62x51mm to 5.56×45mm to reduce recoil and improve rates of fire.
Recently this policy has been reversed somewhat as the 7.62 round is considered more effective in current conflicts.
In other words, some US military units would prefer to go back to using the older heavier calibre that is effective at longer ranges.
However there are a very large number of US and European made assault rifles that take the larger calibre ammunition - so this by itself is not a reason for using AK47s.
US Elite Units
US armed forces include a large number of units that have been described as elite. The Spiegel claim is therefore extremely vague.
Navy Seals use a huge variety of assault weapons including
Colt M4 Carbine
Fabrique Nationale FN Minimi
Fabrique Nationale FN SCAR (Mk 16 / Mk 17)
Heckler & Koch HK 416
Heckler & Koch HK 417
Heckler & Koch HK MP5 (and many variants)
Chinese Type 56 AR
The last of these is an AK47 clone. There are reports of the Seals having purchased Chinese made AK47 clones (but not the Kalashnikov manufactured units).
BOTH THE U.S. NAVY SEALS & FINLAND CHOSE NORINCO stamped type 56 AKM rifles.
The AK 47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the Soviet Union by Mikhail Kalashnikov. The SEALs have the AK 47 in the inventory for a variety of missions. It is one of the most reliable weapons ever made and makes for a great choice when having to swim a weapon over the beach.
It isn't too surprising that
Some special forces units may be trained to be able to pick up and use weapons dropped by their enemies. Therefore they may buy such weapons for training purposes at least.
Some special forces units have access to an enormous range of weapons which they select from according to mission type. The AK47 may be just one of dozens (if not hundreds) of different types of rifle available to them, and may be used occasionally.