Hi
No, the G150 is not single pilot certified. In my view, the G150 (or the G100 for that matter) is a far superior aircraft to the Hawker. Much faster, more range, exceptional baggage capability. G150 also pro line 21.
The G100 and the G150 have no wet footprint for a west coast to Hawaii when Universal worked it out for us. MMO for the G100 is M0.875 and the G150 is M0.850, pretty quick aircraft. The Hawker has better short field perf (I believe) but is nowhere near as quick.
Good luck with the decision. At least you're working for someone who is still looking at spending an aviation budget!