Disabling echi driver in UKC does the trick. OpenBSD is fully functional
on Wyse C90LE. 

I want to warn people about one thing. The Thin client in question 
comes with Chrome video card. It looks like Open Chrome driver doesn't
support the particular video chip-set. I was running X on VESA driver
which is obviously not desirable. I am not sure if there is bug in 
Open Chrome driver or just chip-set (I think it was 11 when I looked
at xorg.log).

I sent dmesg to dmesg AT openbsd and I sent one to misc but I think 
MARK's server bounced me as a spam since it was sent from dynamic IP 
without reverse DNS.

If anybody needs any information about this do not hesitate to send me a
private e-mail.

Predrag