I think you can, just they can't be in your final elite 4 beating party. I could be wrong, but that's the impression I got.
Yeah, that sounds logical. You need 2 HM slaves at least if you don't want to use HMs on your final party, you can't get one pokemon that can learn both fly and surf for example.
Update: :)
Aim:
Gyarados
Hypno
Marowack
Poliwrath
Hitmonchan
Lickitung
First:
Pikachu/Peek lvl 5 -- Thundershock - Growl -
"image removed"
HP 18
ATT 11
DEF 8
SPD 15
SPC 10
Battled Gary and won. Peek reached lvl 6 and learned Tail Whip.
Caught a Mankey on Route 22.
Mankey/Monkee lvl 6 -- Scratch - Leer -
"image removed"
HP 22
ATT 16
DEF 10
SPD 13
SPC 9
End of session location: Viridian Forest. Pokemon: Pikachu/Peek lvl 7, Mankey/Monkee lvl 8.
No team pokemon obtainable yet.
Session 2:
Peek grew to lvl 8 in Viridian Forest and learned Thunder Wave.
Monkee grew to lvl 9 in Viridian Forest and learned Low Kick.
Battled Gary. Beat lvl 9 Spearow with lvl 8 Pikachu/Peek. Beat lvl 8 Eevee with lvl 11 Mankey/Monkee. Won the battle. Team status:
Pikachu/Peek lvl 9 -- Thundershock - Growl - Tail Whip
"image removed"
HP 26/26
ATT 17
DEF 12
SPD 24
SPC 14
Mankey/Monkee lvl 11 -- Scratch - Leer - Low Kick -
"image removed"
HP 32/32
ATT 25
DEF 14
SPD 21
SPC 13
Battled Brock. Beat lvl 10 Geodude with lvl 12 Mankey/Monkee. Beat lvl 14 Onyx with lvl 12 Mankey/Monkee. Won the battle. Recieved the Boulderbadge. Team status:
Pikachu/Peek lvl 9 -- Thundershock - Growl - Tail Whip
"image removed"
HP 26/26
ATT 17
DEF 12
SPD 24
SPC 14
Mankey/Monkee lvl 13 -- Scratch - Leer - Low Kick -
"image removed"
HP 29/36
ATT 29
DEF 16
SPD 25
SPC 15
Deposited Monkee in Pewter City Pokemon Centre PC.
Peek grew to lvl 11 in Viridian Forest and learned Quick Attack.
Bought Magikarp for $5000.
Magikarp/Hydro lvl 5 -- Splash -
"image removed"
HP 18
ATT 6
DEF 10
SPD 13
SPC 7
End of session location: Mt.Moon Pokemon Centre. Pokemon: Pikachu/Peek lvl 14, Magikarp/Hydro lvl 5. Obtained 1 team pokemon. Must use a non-team pokemon to train it (only has Splash).