As you stated, V-tail has some advantages and some disadvantages when compared to conventional tail assembly. In case of UAVs the disadvantages are negligible, leading to them being a relatively common choice.
The advantages of V-tails are that they have fewer surfaces and (thus) fewer intersections, and they are lighter than a comparable conventional tail. All of these lead to less induced and parasitic drag, enhancing the efficiency of the overall design.
The downsides are susceptibility to yawing and more complex control arrangements with "fly-by-cable". To achieve the same stability as a comparable conventional arrangement, a longer rear fuselage is required.
On UAVs the control system is essentially direct drive, so control logic is managed by software instead of relatively complex arrangement of cables, pushrods and pulleys (as in the V-tail Bonanza [IIRC]). Software can also easily address any issue with stability, and since high maneuverability is not top priority in UAVs, control logic can be programmed as quite "conservative". Basically UAVs are not put into extreme flight conditions, so the adverse properties of V-tail are not an issue.