Yes combining treatments can definitely be done and can also give enhanced results. For Hydrafacial and Microneedling, I would recommend starting with HydraFacial and then microneedling with the AntiOx Solution to allow enhanced absorption of the active ingredients in that solution , such as the Hylauronic Acid for hydration and moisturizing of skin.
Combination therapy many times leads to improved results. In regards to combining Hydrafacial and microneedling at the same session, this could be true if the indication is collagen induction plus clarity of skin (for example acne and acne scarring together). However, if you are doing Hydrafacial and microneedling to better control acne and/or for clearer skin, I would suggest alternating and doing them separately to enjoy longer lasting results. Microneedling can reduce sebum production (ie make the skin less oily) and enhance delivery of topical treatments to the skin. Hydrafacial can extract clogged pores and remove the most superficial layer of the skin while infusing a clarifying solution. Either treatment should lead to clearer skin independently for about 4-6 weeks at which point another session would be warranted. If used in combination, results may be enhanced but the longevity of clearer skin would likely remain at 4-6 weeks.