Trying to install Zenphoto v1.4.2-RC1 I get:

Warning!

Version 5.0.0 or greater is required. Version 5.3 or greater is strongly recommended. Use earlier versions at your own risk.

Unfortunately my host offers only PHP Revision 5.2.6 (I am on 5.2.5 now)

So should I expect any problems?

No, as the note says it is recommended not required. Since 5.3 is the official version currently we develop on it to be future save. If there are any issues let us know.

As a note, my box is still at 5.2.17 and works fine.