As things stand, the EliteBook Ultra G1i is not a touch or pen-enabled device; neither the HP website nor current retailer specifications mention a touch-sensitive display or pen mode. Most EliteBook Ultrabooks in this series are classic notebooks without a digitiser.
Conclusion: An active stylus (such as HP Active Pen or similar MPP, AES or N-Trig pens) is not compatible with this model, as the display does not offer pen support.