In general, yes. Mixing oil brands, types (synthetic, semi-synthetic and mineral) and viscosities is fine. For example, you can use a Motul oil to top-up your engine oil when another brand was used for the oil change. Clearly you want to use an oil of the right viscosity and specification, but in terms of oils mixing, the only problem is that the quality of the better oil is diluted by the lesser one. There are a few exceptions; Castor and plant based shouldn't be mixed with conventional oils.