etherI've seen some people use larger FOV's still. When you spec them it actually shows the weird fov.
Does the anti cheat thing not like it or something?
If the server has some kind of plugin that allows changing FOV(TFtrue for example if tftrue_fov is set to higher than 90) then you will see it when you spectate the player. Other than that if you see someone using a higher FOV its probably external plugin that one has compiled by himself but that should be more rare since not many people are interested in risking their account with VAC ban for a higher FOV.
Pretty silly that the game still has FOV limit at 90 when you can just use a custom resolution and gain you a notable advantage towards other players as long as the server has sv_restrict_aspect_ratio_fov set to 0(which ETF2L configs have, dont know bout UGC or ESEA configs).
This is how process mid looks like with my normal 1920x1980 resolution
http://i.imgur.com/kXqDdg7.jpg
And this is how process mid looks like with 1920x720 custom resolution and server having sv_restrict_aspect_ratio_fov 0