There is a pretty new Hampton Inn less than a mile from Amgen (on Ventu Park). There is also a Courtyard and a TownePlace by Marriott about 1.5 miles away. Those will be your best bets for proximity to Amgen.
In Westlake Village (about 6 miles away, toward LA), there is a Hyatt, Four Seasons, Westlake Village Inn (not a chain), a Residence Inn, and another Hampton Inn. All of those are pretty good.
The Hyatt and Westlake Village Inn have the benefit of being near some good restaurants. The food is generally a bit better on the Westlake Village side of things.
Happy to answer any questions about the local area, as are, I am sure, the Amgen folks.
(Full disclosure: our office is across from the Hyatt and I live in Westlake Village, so I might be a little biased.)