Pro: It enables you to mock up a concept and see if it seems like the development path will be easy before you shell out large amounts of money for the real deal.
Cons: It could trap you in a vicious cycle of wiping your virtual machine and re-installing the OS, the trial version, and your product (you do use source control, correct?) if they are hoping that this will alleviate the need for ever paying for the real product.
Suggestion: If you don't mind unsolicited advice, then I would determine why the lead admin wants to use the trial versions -- and then go from there. Until you know the reasons you cannot respond to them.
If they are doing it for the pro reason, then determine if you feel comfortable working with the possibility of switching technologies 30 days into your build. (Can you do it efficiently?)
If they are doing it to avoid spending money, present some of the alternate open source / free options that you are comfortable developing with. If they will not change their modus operandi at that point, then do what is necessary, knowing what you will be walking away from / getting in to.
(And if you don't mind one more bit of unsolicited advice -- if they are doing it for the con reason and will not change WALK AWAY)