'Practice' balls are fine - they are considered logo-ed ones.
X-Outs are allowed whenever the One-Ball or Conforming Ball is part of the Conditions of Competition. This is probably only specified in 'Elite Amateur' events upward.
Practice balls are not range balls
You can get Practice ProVs that just have a minor paint blemish that you can't see for half the price of normal.
Perfectly good balls..
Pro V1 Practice golf balls are conforming products that differ only due to a cosmetic blemish such as paint, ink or registration of stamping. Pro V1 Practice golf balls do not have any construction or performance deficiencies.
Pro V1 X-Out golf balls are also conforming products. However, they usually have a cosmetic blemish and/or occasionally have a minor physical defect that should not significantly affect its performance. More often than not, the physical condition causing the ball to be stamped as an X-Out is so minute that it is not recognizable by the player.
Both products may be used in the casual round of golf including those with scores posted for handicaps, and most competitions, with the possible exception of high level competitions invoking the Local Rule requiring balls to be on the List of Conforming Golf Balls.
As for whether or not you can use these golf balls during a round of golf, you can refer to the USGA Official Rules on the subject listed below for your reference:
Q: May I use a ball stamped with "Practice" or "X-Out" to play a round of golf?
A: Our present policy provides that if the List of Conforming Golf Balls or the One Ball Condition is in effect, a practice or logo ball may be used provided the other markings on the ball (i.e., pole and seam) correspond exactly to a ball listing on the current List of Conforming Golf Balls. Balls labeled with ''PRACTICE'' or a circled ''P'', are essentially treated as a logo ball (such as a Mickey Mouse emblem). A player's name stamped on the ball is also acceptable. However, the original ball markings (i.e., pole and seam markings) must be readable in order for a Rules Official to determine whether that ball is on the List of Conforming Golf Balls. X-Out balls are not permitted to be used in any competition in which the List of Conforming Golf Balls or the One Ball Condition is in effect. However, if neither of these Conditions are in effect, X-Out balls may be used because all balls are presumed to conform unless they have been tested and found not to conform or are obviously non-conforming (e.g., too small or too heavy). (See Decisions 5-1/4 and US/5-1/101).
As a result of the potential for an X-Out to be non-conforming if tested, we do not recommend using this model during tournament play.