Yep M2.5 screws will work - you just don't get so much 'bite' with them as if using the M2.6 but this is a non-standard thread size - why they used this is beyond me but hey ho. Also, a bit of Loctite 243 threadlocker on the M2.5 size screw may be helpful for belt and braces fixing!!!!
cheers
CaptB